The cascade of cellular events in response to an internal signal or environmental stimulus requires a diversity of molecular participants, ranging from ions to enzymes. Signal transduction pathways frequently activate specific protein kinases, leading to the phosphorylation of particular cellular proteins and subsequent initiation of a multitude of cellular responses. Binding and hydrolysis of nucleotides plays a major role in these activities, and our nucleotide analogs and assays for phosphate-producing enzymes are important tools for signal transduction research and high-throughput screening of compounds that affect signal transduction.

We offer a selection of native and modified biomolecules to aid the researcher in dissecting this highly complex branch of the signal transduction process. In addition to the probes below, we have developed the PiPer and EnzChek assay kits for quantitation of inorganic phosphate and pyrophosphate that are extremely useful for following hydrolysis of nucleotides by various enzymes and of phosphate esters by protein phosphatases. These kits and other kits to measure ATP by chemiluminescence and protein phosphatase activity are described in Detecting Enzymes That Metabolize Phosphates and Polyphosphates—Section 10.3.

Protein Kinase Probes and Assays

Protein kinases are critical players in signal transduction pathways. The fluorometric assay of kinases, however, is not straightforward because ATP-dependent phosphorylation of a fluorescent peptide substrate does not directly lead to appreciable changes in the fluorescence of the product.ref We provide an extensive range of assays for protein kinases that utilize a variety of strategies to detect phosphorylation of peptide and protein substrates (Invitrogen kinase assay platforms—Table 17.1).

Antibody Beacon Tyrosine Kinase Assay Kit

The Antibody Beacon Tyrosine Kinase Assay Kit (A35725) provides a homogeneous solution assay for measuring the activity of tyrosine kinases and the effectiveness of potential inhibitors and modulators.ref The key to this tyrosine kinase assay is a small-molecule tracer ligand labeled with our bright green-fluorescent Oregon Green 488 dye. When an anti-phosphotyrosine antibody binds this tracer ligand to form the Antibody Beacon detection complex, the fluorescence of the Oregon Green 488 dye is efficiently quenched. In the presence of a phosphotyrosine-containing peptide, however, this Antibody Beacon detection complex is rapidly disrupted, releasing the tracer ligand and relieving its antibody-induced quenching (Figure 17.3.1). Upon its displacement by a phosphotyrosine residue, the Oregon Green 488 dye–labeled tracer ligand exhibits an approximately fourfold fluorescence enhancement, enabling the detection of as little as 50 nM phosphotyrosine-containing peptide with excellent signal-to-background discrimination. Key benefits of the Antibody Beacon Tyrosine Kinase Assay Kit include:

  • Real-time measurements. Unlike many other commercially available tyrosine kinase assays, the Antibody Beacon Tyrosine Kinase Assay Kit permits real-time monitoring of kinase activity (Figure 17.3.2). Not only is the Antibody Beacon detection complex rapidly dissociated in the presence of phosphotyrosine residues, but the assay components have been designed to be simultaneously combined, eliminating any delay in the measurements.
  • Simple detection protocol. Tyrosine kinase activity is measured by a simple increase in fluorescence intensity; no special equipment, additional reagents, or extra steps are required. This assay is readily compatible with any fluorescence microplate reader.
  • Use of natural substrates. The Antibody Beacon tyrosine kinase assay utilizes unlabeled peptide or protein substrates, is compatible with substrates that are pre-phosphorylated at serine or threonine (but not at tyrosine) residues and is applicable to the assay of a wide variety of kinases.
  • Compatibility. The anti-phosphotyrosine antibody provided in the Antibody Beacon Tyrosine Kinase Assay Kit is specific for phosphotyrosine residues; assay components such as ATP (up to 1 mM) and reducing agents such as dithiothreitol (DTT, up to 1 mM) do not interfere with this assay. This anti-phosphotyrosine antibody was selected from among several clones to produce the greatest fluorescence enhancement by the kinase-phosphorylated product.
  • Reliability. This tyrosine kinase assay has a broad signal window, indicated by a Z' factor ref of >0.85.

The Antibody Beacon Tyrosine Kinase Assay Kit comes with all the reagents needed to perform this assay, including:

  • Oregon Green 488 dye–labeled tracer ligand
  • Anti-phosphotyrosine antibody
  • Concentrated tyrosine kinase reaction buffer
  • Two generic tyrosine kinase substrate solutions: a poly(Glu:Tyr) solution and a poly(Glu:Ala:Tyr) solution
  • Dithiothreitol (DTT)
  • Adenosine triphosphate (ATP)
  • Phosphotyrosine-containing peptide, phospho-pp60 c-src (521–533), for use as a reference
  • Detailed protocols (Antibody Beacon Tyrosine Kinase Assay Kit)

Each kit provides sufficient reagents to perform ~400 assays using a 50 µL assay volume in a fluorescence microplate reader.

Figure 17.3.1 Reaction scheme for the tyrosine kinase assay used in the Antibody Beacon Tyrosine Kinase Assay Kit (A35725). The unlabeled natural substrate (AIYAE) is phosphorylated by the tyrosine kinase to AIY(P)AE, which displaces the quenched Oregon Green 488 dye–labeled peptide from the anti-phosphotyrosine antibody, resulting in a large increase in its fluorescence that is proportional to the amount of AIY(P)AE formed in the reaction.

Figure 17.3.2 Real-time detection capability of the Antibody Beacon Tyrosine Kinase Assay Kit (A35725). Fluorescence of the Antibody Beacon detection complex in tyrosine kinase assay buffer was monitored over time. After ~15 seconds, an excess of phosphotyrosine-containing peptide was added to the Antibody Beacon detection complex and the off-rate was calculated.

Fluorescent Polymyxin B Analogs

Polymyxin B is a cyclic polycationic peptide antibiotic (Figure 17.3.3) that binds to lipopolysaccharides and anionic lipids.ref Polymyxin B is also a selective inhibitor of protein kinase C, with an IC50 of ~35 µM,ref as well as a potent inhibitor of calmodulin, with an IC50 of 80 nM in the presence of 500 µM Ca2+.ref Our fluorescent polymyxin B analogs include those of the green-fluorescent BODIPY FL ref and Oregon Green 514 fluorophores (P13235P13236), as well as the ultraviolet light–excitable dansyl polymyxin ref (P13238).


Figure 17.3.3. Structure of polymyxin B.


Hypericin (H7476), an anthraquinone derivative isolated from plants of the genus Hypericum,ref is a potent, selective inhibitor of PKC (IC50 = 1.7 µg/mL = 3.4 µM) useful for probing and manipulating PKC in live cells.ref Hypericin has a variety of pharmacological properties, from antibacterial and antineoplastic activities to antiviral activities ref and induction of apoptosis.ref Hypericin is also a potent photosensitizer, with a quantum yield of 0.75 for the generation of singlet oxygen.ref

Protein Phosphatase Assay Kits

RediPlate 96 EnzChek Tyrosine Phosphatase Assay Kits

Protein tyrosine phosphatases (PTP) represent a large family of enzymes that play a very important role in intra- and intercellular signaling. PTPs work antagonistically with protein tyrosine kinases to regulate signal transduction pathways in response to a variety of signals, including hormones and mitogens.ref Our RediPlate 96 EnzChek Tyrosine Phosphatase Assay Kit (R22067) provide researchers with a sensitive and convenient method to monitor PTP and screen PTP inhibitors in a variety of research areas ref (Figure 17.3.4).

The EnzChek tyrosine phosphatase assay is based on 6,8-difluoro-4-methylumbelliferyl phosphate ref (DiFMUP, D6567, D22065; Detecting Enzymes That Metabolize Phosphates and Polyphosphates—Section 10.3). Unlike other end-point tyrosine phosphatase assay kits, the EnzChek tyrosine phosphatase assay is continuous, allowing researchers to easily measure fluorescence at various time points in order to follow the kinetics of the reaction. Furthermore, the assay is not affected by free phosphate and is compatible with most nonionic detergents, minimizing sample processing before analysis. Most importantly, each assay well contains inhibitors to help ensure that the assay is selective for tyrosine phosphatases; other phosphatases, including serine/threonine phosphatases, will not hydrolyze DiFMUP under our assay conditions (Figure 17.3.5). Unlike phosphopeptide-based assays, this DiFMUP-based assay can be used to monitor a variety of tyrosine phosphatases, including PTP-1B and CD-45 (Figure 17.3.5). Tyrosine phosphatase inhibitors can be evaluated quantitatively in the assay for their effect on tyrosine phosphatase activity.

Each RediPlate 96 EnzChek Tyrosine Phosphatase Assay Kit (R22067) includes:


Figure 17.3.4 Schematic diagram of the method used in the RediPlate EnzChek Phosphatase Assay Kits (R22067, R33700).
Figure 17.3.5 Specificity of the RediPlate 96 EnzChek Tyrosine Phosphatase Assay Kit (R22067). The phosphatases listed in the tables were applied to a RediPlate 96 EnzChek tyrosine phosphatase assay microplate. At the indicated time points, the fluorescence was measured in a fluorescence microplate reader using excitation at 355 ± 20 nm and emission at 460 ± 12.5 nm

RediPlate 96 EnzChek Serine/Threonine Phosphatase Assay Kit

The majority of protein phosphorylation occurs on serine and threonine residues, with <0.01–0.05% on tyrosine residues. Serine/threonine phosphatases represent a large family of enzymes that have been implicated in the regulation of metabolism, transcription, translation, differentiation, cell cycle, cytoskeletal dynamics, oncogenesis and signal transduction. The RediPlate 96 EnzChek Serine/Threonine Phosphatase Assay Kit (R33700) provides a fast, simple and direct fluorescence-based assay for detecting serine/threonine phosphatases and their corresponding modulators and inhibitors ref (Figure 17.3.4).

As with the RediPlate 96 EnzChek Tyrosine Phosphatase Kit, the substrate incorporated in the RediPlate 96 EnzChek Serine/Threonine Phosphatase Assay Kit is DiFMUP. Inhibitors are included in each assay well to help ensure that the assay is selective for serine/threonine phosphatases; under the prescribed assay conditions, other phosphatases, including tyrosine phosphatases, do not significantly react with the substrate (Figure 17.3.6). Furthermore, unlike phosphopeptide-based assays, this DiFMUP-based assay can be used to monitor a variety of serine/threonine phosphatases including PP-1, PP-2A and PP-2B (Figure 17.3.6). Serine/threonine phosphatase inhibitors can be evaluated quantitatively in the assay for their effect on serine/threonine phosphatase activity (Figure 17.3.7). Additional advantages of this RediPlate assay include compatibility with nonionic detergents and insensitivity to free phosphate, minimizing sample processing before analysis.

Each RediPlate 96 EnzChek Serine/Threonine Phosphatase Assay Kit includes:

To ensure the integrity of the pre-dispensed reagents, the 96-well microplate provided in both RediPlate Protein Phosphatase Assay Kits is packaged in a resealable foil pouch and consists of twelve removable strips, each with eight wells (Figure 17.3.8). Eleven of the strips (88 wells) are preloaded with the fluorogenic substrate DiFMUP; the remaining strip, marked with black tabs, contains a dilution series of the DiFMU reference standard for generating a standard curve.


Figure 17.3.6
Specificity of the RediPlate 96 EnzChek Serine/Threonine Phosphatase Assay Kit (R33700) for serine/threonine phosphatases. The phosphatases listed in the tables were applied at the indicated concentrations to a RediPlate 96 EnzChek serine/threonine phosphatase assay microplate. Reactions were incubated at 37°C. After 1 hour, fluorescence was measured in a fluorescence microplate reader using excitation at 355 ± 20 nm and emission at 460 ± 12.5 nm


Figure 17.3.7
Detection of PP-2A inhibition by okadaic acid using the RediPlate 96 EnzChek Serine/Threonine Phosphatase Assay Kit (R33700). Each reaction contained 50 µM DiFMUP, 10 mU/mL PP-2A and the indicated concentration (log scale) of okadaic acid in reaction buffer containing 50 mM Tris-HCl, 0.1 mM CaCl2, 1 mM NiCl2, 125 µg/mL bovine serum albumin (BSA) and 0.05% Tween 20. Reactions were incubated at 37°C. After 30 minutes, fluorescence was measured in a fluorescence microplate reader using excitation at 355 ± 20 nm and emission at 460 ± 12.5 nm


Figure 17.3.8
A RediPlate 96 microplate

Pro-Q Diamond Phosphoprotein/Phosphopeptide Microarray Stain Kit

The Pro-Q Diamond Phosphoprotein/Phosphopeptide Microarray Stain Kit (P33706) provides a method for selectively staining phosphoproteins or phosphopeptides on microarrays without the use of antibodies or radioactivity. This kit permits direct detection of phosphate groups attached to tyrosine, serine or threonine residues in a microarray environment and has been optimized for microarrays with acrylamide gel surfaces. Each Pro-Q Diamond Phosphoprotein/Phosphopeptide Microarray Stain Kit provides:

The Pro-Q Diamond Phosphoprotein/Phosphopeptide Microarray Stain Kit is ideal for identifying kinase targets in signal transduction pathways and for phosphoproteomics studies.ref

Adenylate Cyclase Assays

3',5'-Cyclic AMP (cAMP) is an important second messenger in many signal transduction pathways, linking activation of cell-surface membrane receptors to intracellular responses, and ultimately, to changes in gene expression. cAMP is synthesized by plasma membrane–bound adenylate cyclase, which is coupled to transmembrane receptors for hormones, neurotransmitters and other signaling molecules by heterotrimeric G-proteins. Upon ligand binding, the intracellular receptor domain of a G-protein–coupled receptor (GPCR) interacts with a G-protein, which then dissociates and activates adenylate cyclase, resulting in an increase in the concentration of intracellular cAMP. Subsequently, cAMP activates cAMP-dependent protein kinases (protein kinase A), which phosphorylate specific substrate proteins, including enzymes, structural proteins, transcription factors and ion channels.

Adenylate Cyclase Probe: BODIPY FL Forskolin

Forskolin, isolated from Coleus forskohlii, is a potent activator of adenylate cyclase, the enzyme that catalyzes the formation of cAMP from ATP. Green-fluorescent BODIPY FL forskolin (B7469) has been used to visualize adenylyl cyclase internalization and subcellular distribution,ref as well as for the pharmacological characterization of adenylyl cyclase catalytic subunits.ref

cAMP Chemiluminescent Immunoassay Kit

The cAMP Chemiluminescent Immunoassay Kit enables ultrasensitive determination of 3',5'-cyclic AMP (cAMP) levels in cell lysates, providing the highest sensitivity of any commercially available cAMP assay. As few as 60 femtomoles of cAMP can be detected. Furthermore, this assay has a wide dynamic range, detecting from 0.06 to 6000 picomoles without the need for sample dilution or manipulations such as acetylation. This extensive dynamic range is especially important in cell-based assays designed to measure Gs- or Gi-coupled agonist stimulation or inhibition. Intra-assay precision for duplicate samples is typically 5% or less.

This competitive immunoassay is formatted with maximum flexibility to permit either manual assay or automated high-throughput screening. The cAMP immunoassay is based on the highly sensitive CSPD alkaline phosphate substrate, a chemiluminescent 1,2-dioxetane, with Sapphire-II luminescence enhancer. The ready-to-use substrate⁄enhancer reagent generates sustained glow light emission that is measured 30 minutes after addition. Once the substrate⁄ enhancer reaches the glow signal, the plate can be read for hours with little or no degradation of the signal, facilitating screening protocols in which several plates are compared to each other. In addition, the assay exhibits exceptionally low crossreactivity with other adenosine containing or cyclic nucleotides.

The cAMP Chemiluminescent Immunoassay Kit (2-plate size, C10557; 10-plate size, C10558) is designed for the rapid and sensitive quantitation of cAMP in extracts prepared from mammalian cells cultured in microwell plates. Each kit provides all required reagents, including:

  • Alkaline phosphate conjugate of cAMP
  • Anti-cAMP antibody
  • cAMP standard
  • CSPD substrate and Sapphire-II luminescence enhancer
  • Assay and lysis buffer
  • Conjugate dilution buffer
  • Wash buffer
  • Pre-coated microplates
  • Detailed protocols (cAMP Chemiluminescent Immunoassay Kit)

The cAMP Chemiluminescent Immunoassay Kit is designed for quantitating cellular cAMP for functional assays of receptor activation. It has been used with established cell lines for functional measurements with endogenous receptors,ref with cell lines containing exogenously expressed ligand receptors,ref with primary cells ref and with tissues.ref It has also been used for receptor characterization,ref orphan receptor ligand identification ref and the characterization of novel chimeric receptors.ref In addition, this assay can be used for high-throughput screening assays ref of compounds that stimulate or interfere with these signal transduction pathways.

Nucleotide Analogs

Nucleotide analogs that serve as substrates or inhibitors of enzymes, as well as nucleotide derivatives that selectively bind to regulatory sites of nucleotide-binding proteins, have been used as structural and mechanistic probes for isolated proteins, reconstituted membrane-bound enzymes, organelles such as mitochondria, and tissues such as skinned muscle fibers.ref More recently, however, these analogs have also been employed to study the effects of nucleotides on signal transduction and to screen for compounds that may affect signal transduction, such as G protein inhibitors and activators (G proteins and GTP Analogs for Binding Studies—Note 17.1).

We prepare a variety of nucleotide analogs, including:

  • Alexa Fluor derivatives of cAMP for use as probes of type I cAMP-dependent protein kinases (PKA I) and Alexa Fluor 647 ATP (A22362)
  • BODIPY dye–labeled nucleotides for use as enzyme substrates and as long-wavelength probes of nucleotide-binding sites
  • Environment-sensitive, blue-fluorescent N-methylanthraniloyl (MANT) nucleotides
  • Blue-fluorescent ethenoadenosine triphosphate (ε-ATP, E23691)
  • Environment-sensitive trinitrophenyl (TNP) nucleotides
  • Caged nucleotides, which are important probes for studying the kinetics and mechanism of nucleotide-binding proteins because they allow spatial and temporal control of the release of active nucleotide
  • Photoaffinity nucleotides for site-selective covalent labeling
  • Fluorescent ChromaTide nucleotides and aha-dUTP nucleotides,  which are primarily used for biosynthetic incorporation into DNA or RNA (Labeling Oligonucleotides and Nucleic Acids—Section 8.2)

Alexa Fluor cAMP and Alexa Fluor ATP

Our Alexa Fluor cAMP analogs are 8-(6-aminohexyl)amino derivatives; similar analogs have been shown to exhibit a marked preference for binding to type I cAMP-dependent protein kinases (PKA I). We offer the green-fluorescent Alexa Fluor 488 cAMP (A35775) and far-red–fluorescent Alexa Fluor 647 cAMP (A35777). Alexa Fluor 488 cAMP was loaded into cells by electroporation and then used to measure intercellular diffusion of cAMP from regulatory to responder T cells via gap junctions.ref

The Alexa Fluor 647 conjugate of ATP (A22362) comprises the long-wavelength Alexa Fluor 647 fluorophore linked to the ribose of ATP by a urethane bridge. Validated applications of this probe include fluorescence resonance energy transfer (FRET) analysis (Fluorescence Resonance Energy Transfer (FRET)—Note 1.2) of nucleotide association with Na+/K+-ATPase ref and measurements of the catalytic activity of heavy meromyosin.ref

BODIPY Ribonucleotide Di- and Triphosphates

Our selection of BODIPY dye–modified ribonucleotides includes:

  • BODIPY FL adenosine 5'-triphosphate (BODIPY FL ATP, A12410)
  • BODIPY TR adenosine 5'-triphosphate (BODIPY TR ATP, A22352)
  • BODIPY TR adenosine 5'-diphosphate (BODIPY TR ADP, A22359)
  • BODIPY FL guanosine 5'-triphosphate (BODIPY FL GTP, G12411)
  • BODIPY TR guanosine 5'-triphosphate (BODIPY TR GTP, G22351)
  • BODIPY FL guanosine 5'-diphosphate (BODIPY FL GDP, G22360

These mixed-isomer analogs comprise a BODIPY fluorophore attached to the 2' or 3' position of the ribose ring via an aminoethylcarbamoyl linker. Interactions between the fluorophore and the purine base are evident from the spectroscopic properties of these nucleotide analogs. The fluorescence quantum yield of BODIPY FL GTP and BODIPY TR GTP is significantly quenched in solution (Figure 17.3.9) and increases upon binding to at least some GTP-binding proteins.ref Similar nucleotide analogs incorporating fluorophores such as fluorescein, tetramethylrhodamine and Cy3 dye have been primarily used for biophysical studies of nucleotide-binding proteins.ref The BODIPY dye–labeled nucleotides may be particularly useful for fluorescence polarization–based assays of ATP- or GTP-binding proteins.


Figure 17.3.10
Principle of fluorescence-based detection of the diadenosine triphosphate hydrolase activity of Fhit using BODIPY FL GTP-γ-S thioester (G22183) as a substrate analog.

Nonhydrolyzable BODIPY ATP and GTP Analogs

Among the most useful fluorescent nucleotides for protein-binding studies are those that stoichiometrically bind to ATP- or GTP-binding sites but are not metabolized. We offer the following nonhydrolyzable BODIPY nucleotides:

  • BODIPY FL AMPPNP ref (B22356)
  • BODIPY FL ATP-γ-S (A22184)
  • BODIPY FL GTP-γ-S ref (G22183)
  • BODIPY 515/530 GTP-γ-S (G35779)
  • BODIPY TR GTP-γ-S (G35780)
  • BODIPY FL GTP-γ-NH amide (G35778

The fluorescence of the BODIPY GTP-γ-S thioesters is quenched ~90% relative to that of the free dye but is recovered upon protein binding to G-proteins.ref The green-fluorescent BODIPY FL GTP-γ-S has been used to detect GTP-binding proteins separated by capillary electrophoresis.ref As compared with BODIPY FL GTP-γ-S thioester, the green-fluorescent BODIPY 515/530 GTP-γ-S thioester has a greater fluorescence increase upon protein binding, . The BODIPY TR GTP-γ-S thioester is a red-fluorescent analog with spectral properties similar to the Texas Red dye.

Although BODIPY FL GTP-γ-NH amide exhibits less fluorescence enhancement upon protein binding, it is reportedly the best of the three green-fluorescent GTP-γ analogs for directly monitoring nucleotide exchange.ref The different linker lengths of the green-fluorescent GTP-γ analogs (six-carbon for BODIPY FL GTP-γ-NH amide, four-carbon for BODIPY FL GTP-γ-S and one-carbon for BODIPY 515/530 GTP-γ-S) may be useful for understanding protein active-site geometries.

In addition to their potential use for binding studies, BODIPY FL ATP-γ-S and BODIPY FL GTP-γ-S thioesters are important substrates for Fhit (Figure 17.3.10), a member of the histidine triad superfamily of nucleotide-binding proteins that bind and cleave diadenosine polyphosphates.ref Fhit, one of the most frequently inactivated proteins in lung cancer, functions as a tumor suppressor by inducing apoptosis.ref These BODIPY nucleotides should be especially useful for screening potential Fhit inhibitors and activators.


N-Methylanthraniloyl (MANT) Nucleotides

The blue-fluorescent MANT nucleotide analogs of ATP, AMPPNP, GTP, GMPPNP, ADP and GDP are modified on the ribose moiety, making these probes particularly useful for studying nucleotide-binding proteins that are sensitive to modifications of the purine base.ref The compact nature of the MANT fluorophore and its attachment position on the ribose ring results in nucleotide analogs that induce minimal perturbation of nucleotide–protein interactions, as confirmed by X-ray crystal structures of MANT nucleotides bound to myosin ref and H-ras p21.ref Furthermore, because MANT fluorescence is sensitive to the environment of the fluorophore, nucleotide–protein interactions may be directly detectable. These properties (Spectroscopic properties of MANT-ATP in aqueous solution (pH 8)—Table 17.2) make MANT nucleotides valuable probes of the structure and enzymatic activity of nucleotide-binding proteins.ref

Applications for MANT-ATP (M12417), MANT-ADP (M12416) and MANT-AMPPNP (M22354) include analysis of:


  • ATPase kinetics of kinesin ref and other microtubule motor-proteins ref using stopped-flow fluorescence measurements
  • Conformation of the myosin subfragment-1 nucleotide-binding site, as indicated by fluorescence quencher accessibility ref
  • Interaction of P-glycoprotein ATP-binding sites with drug efflux–modulating steroids ref
  • Myosin ATPase activity in rabbit skeletal muscle ref
  • Structural characteristics of the nucleotide-binding site of Escherichia coli DnaB helicase ref


Applications for MANT-GTP (M12415), MANT-GDP (M12414) and MANT-GMPPNP (M22353) include analysis of:


  • Activation of protein kinases by Rho subfamily GTP-binding proteins ref
  • Conformational changes during activation of heterotrimeric G-proteins ref
  • Effects of nucleotide structural modifications on binding to H-ras p21 ref
  • Nucleotide hydrolysis and dissociation kinetics of H-ras p21 and other low molecular weight GTP-binding proteins ref
  • GTP-binding proteins Rab5 and Rab7,ref Raf-1,ref Rho ref and Rac,ref as well as Ras-related proteinsref


Ethenoadenosine Nucleotide

The ethenoadenosine nucleotides—developed in 1972 by Leonard and collaborators ref—bind like endogenous nucleotides to several proteins. The properties and applications of ethenoadenosine and MANT nucleotides have been comprehensively reviewed.ref The etheno ATP analog (ε-ATP, E23691) can often mimic ATP in both binding and function. This probe has been used to replace ATP in actin polymerization reactions ref and is frequently incorporated in place of the tightly bound actin nucleotide.ref It also supports contraction of actomyosin, facilitates the measurement of nucleotide-exchange kinetics in actin ref and serves as a substrate for myosin, which converts it to ε-ADP.ref Sensitized luminescence of Tb3+ (T1247Polar Tracers—Section 14.3) coordinated to ε-ATP is a sensitive probe of binding to the catalytic site of protein disulfide isomerase.ref

Trinitrophenyl (TNP) Nucleotides

Unlike the etheno derivatives, the free trinitrophenyl (TNP) nucleotides are essentially nonfluorescent in water. The TNP nucleotides undergo an equilibrium transition to a semiquinoid structure that has relatively long-wavelength spectral properties;ref this form is only fluorescent when bound to the nucleotide-binding site of some proteins. The TNP derivative of ATP frequently exhibits a spectral shift and fluorescence enhancement upon protein binding and actually binds with higher affinity than ATP to some proteins. The broad, long-wavelength absorption of TNP nucleotides makes them useful for FRET studies ref (Fluorescence Resonance Energy Transfer (FRET)—Note 1.2). The TNP derivatives of ATP (TNP-ATP, T7602), ADP (TNP-ADP, T7601) and AMP (TNP-AMP, T7624) have been used as structural probes for a wide variety of nucleotide-binding proteins.ref We have found that chromatographically purified TNP nucleotides are unstable during lyophilization. Consequently, these derivatives are sold in aqueous solution and should be frozen immediately upon arrival.

Caged Nucleotides

Caged nucleotides are nucleotide analogs in which the terminal phosphate is esterified with a blocking group, rendering the molecule biologically inactive. Photolytic removal of the caging group by UV illumination results in a pulse of the nucleotide—often on a microsecond to millisecond time scale—at the site of illumination. Because photolysis ("uncaging") can be temporally controlled and confined to the area of illumination, the popularity of this technique is growing. We are supporting this development by synthesizing a variety of caged nucleotides, neurotransmitters and Ca2+ chelators. Our current selection of caged nucleotides includes:



Photoactivatable Reagents, Including Photoreactive Crosslinkers and Caged Probes—Section 5.3 discusses our selection of caged probes and the properties of the different caging groups that we use (Properties of six different caging groups—Table 5.2).

Researchers investigating the cytoskeleton have benefited greatly from advances in caging technology, primarily originating from the work of Trentham, Kaplan and their colleagues.ref NPE-caged ADP (A7056) is a useful probe for studying the effect of photolytic release of ADP in muscle fibers ref and isolated sarcoplasmic reticulum.ref Although it is sometimes difficult to properly abstract papers that describe experiments with caged ATP because they could be referring to either NPE-caged ATP (A1048), DMNPE-caged ATP (A1049) or earlier caged versions of this nucleotide, most researchers have used NPE-caged ATP.

Because the caged nucleotides may be added to an experimental system at relatively high concentrations, use of the enzyme apyrase was recommended by Sleep and Burton ref to eliminate any traces of ATP that may be present in the caged ATP probes.ref Once the caged ATP solutions have been preincubated with apyrase, the enzyme can be removed by centrifugal filtration.ref

These caged nucleotides are generally cell impermeant and must be microinjected into cells or loaded by other techniques (Techniques for loading molecules into the cytoplasm—Table 14.1). Permeabilization of cells with staphylococcal α-toxin or the saponin ester β-escin is reported to make the membrane of smooth muscle cells permeable to low molecular weight (<1000 daltons) molecules, while retaining high molecular weight compounds.ref α-Toxin permeabilization has permitted the introduction of caged nucleotides, including caged ATP (A1048) and caged GTP-γ-S, as well as of caged inositol 1,4,5-triphosphate (NPE-caged Ins 1,4,5-P3I23580Calcium Regulation—Section 17.2) into smooth muscle cells.ref Caged inositol 1,4,5-triphosphate has also been successfully loaded in ECV304 cells using electroporation.ref


Functional ion channels can be assembled from both homomeric and heteromeric combinations of the seven P2X receptor subunits so far identified (P2X1–7). Due to the lack of specific agonists or antagonists for P2X receptors, it is difficult to determine which receptor subtypes mediate particular cellular responses. We offer one of the most potent and widely used P2X receptor agonists, BzBzATP ref (2'-(or 3'-)O-(4-benzoylbenzoyl)adenosine 5'-triphosphate, B22358). BzBzATP has more general applications for site-directed irreversible modification of nucleotide-binding proteins via photoaffinity labeling.ref


Data Table

Cat #MWStorageSolubleAbsECEmSolventNotes
A1048700.30FF,D,LLH2O25918,000noneMeOH1, 2, 3
A1049760.35FF,D,LLH2O3514400noneH2O1, 2
A7056614.44FF,D,LLH2O25915,000noneMeOH1, 2, 3
A12410933.30FF,LH2O50554,000514H2O4, 5
A124121117.18FF,LH2O3234200461pH 74, 5, 6
A22184878.28FF,LH2O50468,000514pH 74, 5
A223521065.43FF,LH2O59155,000620pH 74, 5
A22359963.47FF,LH2O59257,000621pH 74, 5
A22362~2050FF,LH2O648246,000667pH 74, 5
A357751162.23FF,LH2O49371,000517pH 74, 5
A35777~1700FF,LH2O649246,000666pH 74, 5
B22356932.31FF,LH2O50468,000514H2O4, 5
B223581018.97FF,LH2O26027,000nonepH 7 
D1037524.38F,D,LLDMSO3386100noneMeOH1, 2
E23691619.13FFH2O2655000411pH 75
G12411949.30FF,LH2O50468,000511H2O4, 5, 7
G22183894.28FF,LH2O50468,000510pH 74, 5, 7
G223511081.43FF,LH2O59156,000620pH 74, 5, 7
G223601005.75FF,LH2O50468,000508pH 74, 5, 7
G35778905.29FF,LH2O50568,000512pH 74, 5, 7
G35779865.28FF,LH2O511 520pH 74, 5, 7
G357801153.60FF,LH2O591 621pH 74, 5, 7
H7476504.45F,D,LDMSO, DMF59137,000594EtOH 
M12414620.32FF,LH2O3565700447pH 84, 5, 8
M12415722.28FF,LH2O3565700448pH 74, 5, 8
M12416604.32FF,LH2O3565800448pH 74, 5, 8
M12417706.28FF,LH2O3565800447pH 74, 5, 8
M22353721.29FF,LH2O3575700447pH 84, 5, 8
M22354705.29FF,LH2O3575800447pH 84, 5, 8
T7601682.26FF,LH2O40826,000nonepH 84, 5, 9
T7602784.22FF,LH2O40826,000nonepH 84, 5, 9
T7624579.29F,LH2O40826,000nonepH 84, 5, 9
  1. Caged nucleotide esters are free of contaminating free nucleotides when initially prepared. However, some decomposition may occur during storage.
  2. All photoactivatable probes are sensitive to light. They should be protected from illumination except when photolysis is intended.
  3. This compound has weaker visible absorption at >300 nm but no discernible absorption peaks in this region.
  4. The molecular weight (MW) of this product is approximate because the degree of hydration and/or salt form has not been conclusively established.
  5. This product is supplied as a ready-made solution in the solvent indicated under "Soluble."
  6. QY = 0.63 in 50 mM Tris, pH 8.0. Fluorescence shifts to longer wavelengths (Em ~475 nm) on enzymatic cleavage of the α–β phosphoryl bond.ref
  7. Fluorescence of BODIPY dye–labeled guanosine derivatives is generally weak due to base-specific intramolecular quenching.ref
  8. Fluorescence quantum yields of MANT nucleotides are environment-dependent. In H2O, QY is ~0.2.ref
  9. Trinitrophenyl nucleotides are in fact very weakly fluorescent in water (Em ~560 nm). Fluorescence is blue-shifted and more intense in organic solvents (DMSO, EtOH) and when bound to proteins (Em ~540 nm). Absorption spectrum also has a second, less-intense, peak at about 470 nm.ref

For Research Use Only. Not for use in diagnostic procedures.