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EDAC, 1-Ethyl-3-(3-Dimethylaminopropyl)carbodiimide, Hydrochloride (Invitrogen™)

EDAC is a water-soluble carbodiimide that can be used to crosslink biological substances that contain carboxylate acids and primary amines. Protocols for crosslinking molecules with this reagent can be found in Bioconjugate Techniques, by G.T. Hermanson (B-7884).

Sulfo-KMUS (N-κ-maleimidoundecanoyl-oxysulfosuccinimide ester) (Thermo Scientific™)

Thermo Scientific Pierce Sulfo-KMUS is a water-soluble amine-to-sulfhydryl crosslinker that contains NHS-ester and maleimide reactive groups at opposite ends of a long spacer arm (16.3 angstroms).

Features of Sulfo-KMUS:

Reactive groups: sulfo-NHS ester and maleimide
Reactive toward: amino and sulfhydryl groups
• Long aliphatic spacer arm compared to Sulfo-GMBS
• Sulfo-NHS ester reacts with primary amines at pH 7-9, forming a stable amide bond
• Maleimide reacts with -SH groups at pH 6.5-7.5, forming a stable thioether bond
• Non-cleavable
• Water-soluble

Product References:
Crosslinker Application Guide -- search for recent literature references for this product

Pierce™ Premium Grade Sulfo-NHS (N-hydroxysulfosuccinimide) (Thermo Scientific™)

Thermo Scientific Pierce Premium Grade Sulfo-NHS is our highest quality formulation of this N-hydroxysuccinimide chemical modification reagent, specially characterized for applications where product integrity and risk minimization are paramount.

Features of Premium Grade Sulfo-NHS:

Sulfo-NHS—use with EDC crosslinker to prepare amine-reactive NHS ester reagents
High quality—identity and purity confirmed by several tests, including quantitative NMR
Product integrity—enhanced level of testing and characterization compared to standard grade
Lot retention—ample supply of past lots retained to ensure future process testing
Change management—Change Control Notification (CCN) service
Consistent manufacture—batch-specific manufacturing documentation review

Applications:
• Improve efficiency of EDC coupling reactions
• Convert carboxyls to amine-reactive sulfo-NHS esters
• Membrane-impermable for cell surface labeling
• Crosslink proteins to carboxyl-coated beads or surfaces more efficiently
• Activate nanoparticles with amine-reactive sulfo-NHS esters

Compared to the standard grade product, Premium Grade Sulfo-NHS provides more clearly defined quality and product support by including (a) increased analytical testing and product characterization, (b) greater batch-specific information and quality assurance review, (c) extensive lot sample retention and (d) change control notification. Sulfo-NHS (N-hydroxysulfosuccinimide) enables control and modification of carbodiimide crosslinking reactions involving activation of carboxylates (—COOH) for conjugation with primary amines (—NH2). Derivatives are easily synthesized by mixing the sulfo-NHS with a carboxyl-containing molecule and a dehydrating agent such as the carbodiimide EDC (EDAC). The method is the basis for generating many types of protein labeling reagents, including amine-reactive fluorescent dyes, biotin affinity tags and pegylation compounds.

Product References:
Crosslinker Application Guide -- search for recent literature references for this product

Related Products
Sulfo-NHS (N-hydroxysulfosuccinimide)
Pierce™ Premium Grade EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride)

SM(PEG)6 (PEGylated, long-chain SMCC crosslinker) (Thermo Scientific™)

Thermo Scientific Pierce SM(PEG)n is a series of amine-to-sulfhydryl crosslinkers that differ in length from 17.6 to 95.2 angstroms as a result of polyethylene glycol spacer arms containing n equals 2 to 24 ethylene glycol units.

Features of SM(PEG)6:

Reactive groups: NHS ester and maleimide
Reactive toward: amino and sulfhydryl groups
• Irreversibly crosslink proteins or peptides by flexible PEG spacer arms
• Polyethylene glycol spacer arms help maintain conjugate solubility
• Pure compound with defined structure and molecular weight, ensuring reproducible protein-modification effects
• PEG spacer provides unique advantages, including increased stability, reduced tendency toward aggregation and reduced immunogenicity
• Ideal for performing controlled, two-step protein conjugations (see Sulfo-SMCC)

SM(PEG)n NHS- and maleimide-activated PEG compounds for crosslinking between primary amines (NH2) and sulfhydryl (SH) groups in proteins and other molecules. A complete set of compounds are offered, each having the same heterobifunctional structure (NHS-PEGn-Maleimide) but differing in the number of discrete ethylene glycol units ( n = 2, 4, 6, 8, 12 or 24). The N-hydroxysuccinimide ester (NHS) group reacts specifically and efficiently with lysine and N-terminal amino groups at pH 7-9 to form stable amide bonds. The maleimide group reacts with reduced sulfhydryls at pH 6.5-7.5 to form stable thioether bonds.

Alternative Names for SM(PEG)n:
• NHS-dPEG-Mal
• Mal-PEG NHS ester
• NHS-PEO-Maleimide
• Succinimidyl-dPEG-maleimide
• Succinimide-Maleimide PEG

Why use crosslinkers with polyethylene glycol (PEG) spacer arms?
PEG-containing reagents have been used to modify proteins to provide specific advantages. Protein PEGylation can improve the stability of the modified protein, protect it from proteolytic digestion, increase its half life in a biological application, mask it from causing an immunogenic response, decrease its antigenicity or potential toxicity, improve its solubility, diminish the potential for aggregation, and minimize interference for both in vitro and in vivo applications. Polyethylene glycol has these effects because it is nontoxic, nonimmunogenic, hydrophilic, water soluble and highly flexible.

Advantages of discrete-length polyethylene glycol compounds:
These reagents are specially synthesized, resulting in homogeneous compounds of defined molecular weight, characterized by discrete chain lengths, providing a greater ability to optimize and characterize surface protein modifications. Typical preparations of PEG compounds are a heterogeneous mixtures composed of a distribution of chain lengths with a specified average molecular weight or approximate number of PEG subunits.

Related Products
SM(PEG)2 (PEGylated SMCC crosslinker)
SM(PEG)4 (PEGylated SMCC crosslinker)
SM(PEG)8 (PEGylated, long-chain SMCC crosslinker)

BMB (1,4-bismaleimidobutane) (Thermo Scientific™)

Thermo Scientific Pierce BMB is a mid-length, maleimide crosslinker for covalent, irreversible conjugation between sulfhydryl groups (e.g., protein or peptide cysteines).

Features of BMB:

Reactive groups: maleimide (both ends)
Reactive towards: sulfhydryl groups
• Mid-length (10.9Å), sulfhydryl-to-sulfhydryl crosslinker, composed of maleimide groups and 9-atom spacer arm
• Water-insoluble—dissolve first in DMF or DMSO, then add to aqueous reaction buffers
• Noncleavable

Related Products
BMH (bismaleimidohexane)
BMOE (bismaleimidoethane)
BM(PEG)2 (1,8-bismaleimido-diethyleneglycol)
BM(PEG)3 (1,11-bismaleimido-triethyleneglycol)

BM(PEG)3 (1,11-bismaleimido-triethyleneglycol) (Thermo Scientific™)

Thermo Scientific Pierce BM(PEG)3 is a bismaleimide-activated PEG compound for crosslinking between sulfhydryl (—SH) groups in proteins and other thiol molecules. The maleimide groups at either end of the PEG3 spacer react specifically and efficiently with reduced sulfhydryls at pH 6.5-7.5 to form stable thioether bonds.

Features of BM(PEG)3:

Reactive groups: maleimide (both ends)
Reactive towards: sulfhydryl groups
• Long, pegylated, sulfhydryl-to-sulfhydryl crosslinkers, composed of maleimide groups and 3-unit polyethylene glycol spacer arm
• PEG spacers provide unique advantages, including enhanced solubility, increased stability, reduced tendency toward aggregation and reduced immunogenicity
• Pure compounds with defined structure and molecular weight, ensuring reproducible protein-modification effects
• Ideal for small molecule or peptide conjugations

Alternative Names for BM(PEG)n:

• Bismaleimide-dPEG
• Mal-PEG-Mal
• BM(PEO)2
• BM-PEO3

Product References:

Crosslinker Application Guide -- search for recent literature references for this product

Related Products
BMB (1,4-bismaleimidobutane)
BMH (bismaleimidohexane)
BMOE (bismaleimidoethane)
BM(PEG)2 (1,8-bismaleimido-diethyleneglycol)

SMPB (succinimidyl 4-(p-maleimidophenyl)butyrate) (Thermo Scientific™)

Thermo Scientific Pierce SMPB is an amine-to-sulfhydryl crosslinker that contains NHS-ester and maleimide reactive groups at opposite ends of a medium-length aromatic spacer arm (11.6 angstroms).

Features of SMPB:

Reactive groups: NHS ester and maleimide
Reactive towards: amino and sulfhydryl groups
• Extended chain analog of MBS
• Non-cleavable
• Water-insoluble (dissolve first in DMF or DMSO)
• Conjugates formed with SMPB are more stable in serum than SPDP conjugates

Product References:
Crosslinker Application Guide -- search for recent literature references for this product

Related Products
Sulfo-SMPB (sulfosuccinimidyl 4-(N-maleimidophenyl)butyrate)

Sulfo-SBED Biotin Label Transfer Reagent, No-Weigh™ Format (Thermo Scientific™)

The Thermo Scientific Pierce Sulfo-SBED Biotin Label Transfer Reagent is a multifunctional reagent for labeling a purified protein and then covalently transferring the attached biotin tag onto specific interactors of that protein.

Sulfo-SBED is the abbreviation for Sulfo-N-hydroxysuccinimidyl-2-(6-[biotinamido]-2-(p-azido benzamido)-hexanoamido) ethyl-1,3'-dithioproprionate. It is a heterobifunctional chemical crosslinker capable of covalently attaching to primary amines at one end and to nearly any protein functional group at the other end. Unlike typical crosslinkers, Sulfo-SBED also includes a biotin group and a cleavable disulfide spacer arm. Together these features allow one to sequentially crosslink interacting proteins and transfer the biotin affinity tag from one protein (i.e., a purified "bait" protein) to another (possibly unknown "prey" protein). Label Transfer is a powerful in vitro method for protein interaction discovery. A growing number of publications feature the use of Sulfo-SBED Biotin Label Transfer Reagent to identify previously unknown protein interaction binding partners and to more fully characterize the specific protein binding domains of other protein interactions.

Typical protocol for label transfer experiment:

• Add a few microliters of dissolved Sulfo-SBED Reagent to 0.5-1 mL of purified bait protein in PBS.
• Incubate mixture for 30-120 minutes on ice or at room temperature in the dark.
• Desalt or dialyze (in subdued light) to remove excess non-reacted Sulfo-SBED from the labeled bait protein.
• Add labeled bait protein to cell lysate or other solution containing putative target protein interactors ("prey").
• When interaction complexes have formed, expose the solution to ultraviolet light (365 nm) for several minutes.
• Analyze products by one of several methods:
Western Blotting: Cleave crosslinks in DTT, separate proteins by SDS-PAGE, and detect biotinylated bands by Western blotting with streptavidin-HRP.
Purification and Mass Spec or Sequencing: Affinity-purify biotinylated proteins or peptide fragments following trypsin digestion and perform MS or sequencing to characterize the proteins involved.

Related Products
Sulfo-SBED Biotin Label Transfer Kit - Western Blot Application

PEG4-SPDP (PEGylated, long-chain SPDP crosslinker) (Thermo Scientific™)

Thermo Scientific Pierce PEG4-SPDP is a multifunctional crosslinker for protein conjugation via amine-to-amine or amine-to-sulfhydryl crosslinks that contain a 4-unit polyethylene glycol (PEG) group and a reducible (cleavable) disulfide bond.

Features of PEG4-SPDP:

Efficient amine conjugationNHS ester provides effective conjugation to lysines, N-termini of peptides and other primary amines
Reversible sulfhydryl conjugationpyridyldithiol group enables disulfide linkage with reduced cysteines and other sulfhydryl groups, providing a stable but cleavable bond
Polyethylene glycol—PEG groups are flexible, non-immunogenic, hydrophilic, and often enhance the solubility of attached molecules
Spacer arm—connects primary amines and sulfhydryl targets at distances up to 25.7 angstroms; compare to PEG12-SPDP (54.1 angstroms)

SPDP-type reagents have an amine-reactive N-hydroxysuccinimide (NHS) ester at one end and a suflhydryl-reactive 2-pyridyldithiol group at the opposite end. PEG4-SPDP has a 4-unit polyethylene glycol spacer arm, which confers greater solubility to the crosslinker and linked proteins compared to crosslinkers having only hydrocarbon spacers. Pyridyldithiol reagents produce disulfide-containing linkages that can be cleaved with reducing agents such as dithiothreitol (DTT). Crosslinking experiments with SPDP reagents are not limited to those involving proteins. Any of a variety of molecules with primary amines and sulfhydryl groups can be modified or crosslinked using an SPDP reagent.

Conjugation of SPDP reagents to primary amines reactions via the NHS ester is most commonly performed at pH 7 to 8 in phosphate, carbonate/bicarbonate or borate buffer. Other buffers that do not contain primary amines (or thiols or disulfide reducing reagents—see the sulfhydryl reactivity discussion) are also effective.

Reaction with the sulfhydryl-reactive pyridyldithio group can be performed with (simultaneously) or following the amine reaction, and it occurs optimally at pH 7 to 8. The reaction results in pyridine-2-thione displacement, the concentration of which can be determined by measuring the absorbance at 343nm. Reaction buffers must be free of thiols and disulfide reducing agents until quenching or reduction of the 2-pyridyldithio is desired.

Product References:
Crosslinker Application Guide -- search for recent literature references for this product

Related Products
PEG12-SPDP (PEGylated, long-chain SPDP crosslinker)
SPDP (succinimidyl 3-(2-pyridyldithio)propionate)

Pierce™ Premium Grade EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride) (Thermo Scientific™)

Thermo Scientific Pierce Premium Grade EDC is our highest quality formulation of this popular carbodiimide crosslinker, specially characterized for applications where product integrity and risk minimization are paramount.

Features of Premium Grade EDC:

EDC—carbodiimide crosslinker for conjugation between carboxylates and amines
High quality—identity and purity confirmed by several tests
Product integrity—enhanced level of testing and characterization compared to standard grade
Lot retention—ample supply of past lots retained to ensure future process testing
Change management—Change Control Notification (CCN) service
Consistent manufacture—batch-specific manufacturing documentation review

Compared to the standard grade product, Premium Grade EDC provides more clearly defined quality and product support by including (a) increased analytical testing and product characterization, (b) greater batch-specific information and quality assurance review, (c) extensive lot sample retention and (d) change control notification. EDC is 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride, a water-soluble carbodiimide crosslinker that activates carboxyl groups for spontaneous reaction with primary amines, enabling peptide immobilization and hapten-carrier protein conjugation. In the presence of N-hydroxysulfosuccinimide (sulfo-NHS), EDC can be used to convert carboxyl groups to amine-reactive sulfo-NHS esters. This is accomplished by mixing the EDC with a carboxyl containing molecule and adding sulfo-NHS.

Specifications of Premium Grade EDC
We manufacture crosslinking reagents to ensure the highest possible overall product integrity, consistency and performance for the intended research applications.
• Visual: White crystalline powder, free of foreign matter
• Identity: IR scan shows only peaks characteristic of EDC
• Water content: Karl Fischer titration, ≤ 2%
• Trace metals: All metals, including lead, ≤ 50 ppm
• Elemental analysis: Reported values for C, H, and N

Applications:
• Conjugate carboxyl and amino groups among peptides and proteins
• Couple haptens to immunogenic carrier proteins (e.g., attach a peptide to KLH)
Immobilize peptide antigens to affinity-purify antibodies
• Create NHS-activated, amine-reactive labeling compounds
• Crosslink proteins to carboxyl coated beads or surfaces
• Activate nanoparticles with amine-reactive sulfo-NHS esters

Product References:
Crosslinker Application Guide -- search for recent literature references for this product

Related Products
EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride)
Pierce™ Premium Grade Sulfo-NHS (N-hydroxysulfosuccinimide)

DTBP (Wang and Richard's Reagent) (Thermo Scientific™)

Thermo Scientific Pierce DTBP is dimethyl 3,3'-dithiobispropionimidate, a crosslinker that contains amine-reactive imidoester groups around an 8-atom spacer arm, whose central disulfide bond can be cleaved with reducing agents.

Dimethyl dithiobispropionimidate (DTBP) is a homobifunctional, cleavable and membrane permeable crosslinker. It contains an amine-reactive imidoester at each end of an 8-atom spacer arm. Imidoesters react with primary amines at pH 8-10 to form stable amidine bonds. The amidine is protonated and therefore, like the lysine it modified, has a positive charge at physiological pH. Proteins, including antibodies, generally have several primary amines in the side chain of lysine (K) residues and the N-terminus of each polypeptide that are available as targets for imidoester crosslinking reagents.

Features of dimethyl 3,3'-dithiobispropionimidate:

Reactive groups: imidoester (both ends)
Reactive towards: amino groups (primary amines)
• Imidoester reacts rapidly with any primary amine-containing molecule to form amidine bonds
• Cleavable by reduction of spacer arm disulfide bond with DTT, TCEP or other reducing agents
• Compare to DMS (non-cleavable)
• Water-soluble

Applications:
• Reversibly crosslink and stabilize protein-protein interactions
• Stabilize protein interactions prior to ChIP assays to capture indirect protein interactions

DTBP crosslinks can be easily reversed by the addition of 100-150 mM DTT at 37°C for 30 minutes. DMS, the non-cleavable analog of DTBP is available for applications that require a stable, non-cleavable bond. DTSSP, the NHS-ester analog of DTBP is also available for applications that require crosslinking at physiologic pH or greater stability of the crosslinked product at elevated pH. DTBP and DMS have essentially identical crosslinking activity toward primary amines.

Properties of DTBP
• Alternate names: Cleavable DMS
• Molecular formula: C8H18N2O2S2Cl2
• Molecular weight: 309.28
• Spacer arm length: 11.9 Å (8 atoms)
• CAS number: 38285-78-8
• Reactive groups: Imidoesters, react with primary amines at pH 8–10

DTBP Specifications
We manufacture DTBP to the highest specifications to produce the most specific bioconjugates, ensure the integrity of your data and to provide you with the highest degree of consistency. Each lot of DTBP cross-linker is tested to meet the following minimum specifications:
Identity: IR scan shows only peaks characteristic of the structure and functional groups of DTBP
Melting point: begins melting between 170-178°C, melts within a 2°C range

Product References:
Crosslinker Application Guide -- search for recent literature references for this product

Related Products
DMA (dimethyl adipimidate)
DMP (dimethyl pimelimidate)
DMS (dimethyl suberimidate)

EZ-Link™ Sulfo-NHS-Biotin, No-Weigh™ Format (Thermo Scientific™)

Thermo Scientific EZ-Link Sulfo-NHS-Biotin is a short-chain, water-soluble biotinylation reagent for labeling antibodies, proteins and other molecules that have primary amines.

Features of EZ-Link Sulfo-NHS-Biotin:

Protein labeling—biotinylate antibodies to facilitate immobilization, purification or detection using streptavidin resins or probes
Cell surface labeling—biotinylates only surface proteins of whole cells because the negatively charged reagent does not permeate cell membranes
Amine-reactive—reacts with primary amines (-NH2), such as lysine side-chains or the amino-termini of polypeptides
Soluble—charged sulfo-NHS group increases reagent water solubility compared to ordinary NHS-ester compounds
Irreversible—forms permanent amide bonds; spacer arm cannot be cleaved
Very short—spacer arm (total length added to target) is 13.5 angstroms; it consists of the native biotin valeric acid group only.

Sulfo-NHS-Biotin is the shortest of three very similar EZ-Link Reagents that are water-soluble, non-cleavable, and enable simple and efficient biotinylation of antibodies, proteins and any other primary amine-containing macromolecules in solution. Specific labeling of cell surface proteins is another common application for these uniquely water-soluble and membrane impermeable reagents. Differing only in their spacer arm lengths, the three Sulfo-NHS-ester reagents offer the possibility of optimizing labeling and detection experiments where steric hindrance of biotin binding is an important factor. Sulfo-NHS-Biotin is offered in several package sizes and as complete protein labeling kits.

We manufacture biotin reagents to ensure the highest possible overall product integrity, consistency and performance for the intended research applications.

N-Hydroxysulfosuccinimide (NHS) esters of biotin are the most popular type of biotinylation reagent. NHS-activated biotins react efficiently with primary amino groups (-NH2) in alkaline buffers to form stable amide bonds. Proteins (e.g., antibodies) typically have several primary amines that are available as targets for labeling, including the side chain of lysine (K) residues and the N-terminus of each polypeptide.

Varieties of biotin NHS-ester reagents differ in length, solubility, cell permeability and cleavability. Non-sulfonated NHS-biotins are cell permeable but must be dissolved in organic solvent such as DMSO or DMF. Sulfo-NHS biotins (and those with pegylated spacers) are directly water soluble but not membrane permeable. Varieties containing disulfide bonds can be cleaved using reducing agents, enabling the biotin group to be disconnected from the labeled protein.

Related Products
EZ-Link™ Sulfo-NHS-Biotinylation Kit
EZ-Link™ Micro Sulfo-NHS-Biotinylation Kit

Pierce™ Controlled Protein-Protein Crosslinking Kit (Thermo Scientific™)

The Thermo Scientific Pierce Controlled Protein-Protein Crosslinking Kit contains essential crosslinkers, modification reagents and buffers for conjugating antibodies, enzymes and other purified proteins needed as probes.

This crosslinking kit contains everything you need to help you insert an unbreakable molecular bridge between practically any two purified proteins and do it successfully right out of the box.

Features of the Controlled Protein-Protein Crosslinking Kit:

• Easy-to-control, stepwise coupling of two proteins—You are in charge of the chemistry. Stop and restart at convenient points or go to completion. It is your choice.
• Better protocol…logically presented and clearly worded instructions which will be appreciated by novice and expert—Instructions teach the method and chemistry of this crosslinking strategy to the user while providing a high likelihood of success. Great for life scientists attempting to prepare a conjugate or crosslink two proteins for the first time.
• Reliable non-cleavable heterobifunctional crosslinking agent—A very popular choice for a crosslinking agent was selected for the kit offering proven chemistry ,highly stabile intermediates and efficient formation of the target conjugate adding to the ease of use and likelihood of success.
• All reagents necessary to affect the crosslinking—Cuts costs over purchasing "catalog size" packaging of all the components by more than 60%. If it's not in the kit, you don't need it!
• Includes disulfide (S-S) reductants and thiolation reagents—Allows for all possibilities regarding the state of the—SH group on one of the proteins to be coupled.
• Ellman's Reagent colorimetric—SH group determination chemistry built into the protocols—You have the option to see how well your reactions went. eg. determine the extent of—SH introduction or estimate the incorporation of maleimide reactive group.

Related Products
Sulfo-SMCC (sulfosuccinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate)

Sulfo-SIAB (sulfosuccinimidyl (4-iodoacetyl)aminobenzoate) (Thermo Scientific™)

Thermo Scientific Pierce Sulfo-SIAB a water-soluble, mid-length (10.6 angstrom) crosslinker for amine-to-sulfhydryl conjugation via sulfo-N-hydroxysuccinimide (sulfo-NHS) ester and iodoacetyl reactive groups.

Features of Sulfo-SIAB:

Reactive groups: sulfo-NHS ester and iodoacetyl
Reactive toward: amino and sulfhydryl groups
• Non-cleavable
• Water-soluble (compare to SIAB)

Product References:
Crosslinker Application Guide -- search for recent literature references for this product

Related Products
SIAB (succinimidyl (4-iodoacetyl)aminobenzoate)

MBS (m-maleimidobenzoyl-N-hydroxysuccinimide ester) (Thermo Scientific™)

Thermo Scientific Pierce MBS is an amine-to-sulfhydryl crosslinker that contains NHS-ester and maleimide reactive groups at opposite ends of a short aromatic spacer arm (7.3 angstroms).

Features of MBS:

Reactive groups: NHS ester and maleimide
Reactive towards: amino and sulfhydryl groups
• Non-cleavable
• Water-insoluble (dissolve first in DMF or DMSO); compare to Sulfo-MBS
• Popular for forming enzyme immunoconjugates

Product References:
Crosslinker Application Guide -- search for recent literature references for this product

Related Products
Sulfo-MBS (m-maleimidobenzoyl-N-hydroxysulfosuccinimide ester)