Modification reagents for proteins and peptides are chemical agents that are used to modify the amino acid side chains in order to alter the native charges, block or expose reactive binding sites, inactivate functional groups, and change functional groups to create targets for crosslinking and labeling.

Reagent categories Product Function
Modification of the amine group Sulfo-NHS-Acetate Amine-reactive (NHS ester) compound to permanently block primary amines (e.g., protein lysine side chains) to prevent interactions or later conjugation.
Citraconic anhydride Amine-reactive compound (CAS 616-02-4) to reversibly cap lysines and other primary amines with carboxyl groups; stable at pH 7 but hydrolyzes (decouples) at pH 3 to 4.
TFCS Amine-reactive (NHS ester) compound to add a 7-atom spacer arm; the terminal trifluoroacetyl group can be removed later to expose a new primary amine.
Modification of the heterobifunctional groups SATP Short (4.1A), amine-reactive (NHS ester) sulfhydryl-addition reagent; creates stable (protected yet exposable) -SH group for protein crosslinking strategies.
SAT(PEG)4 Long (18.2A), PEGylated form of SATA, an amine-reactive (NHS ester) sulfhydryl-addition reagent; contains 4-unit polyethylene glycol spacer arm.
SATA SATA is a short-chain (2.8 angstrom spacer arm) reagent for covalent modification of primary amines and addition of a protected yet exposable sulfhydryl group, enabling heterobifunctional crosslinking strategies.
SATA Sulfhydryl Addition Kit A complete kit with SATA reagent and hydroxylamine to modify protein primary amines to create free sulfhydryl groups for crosslinking techniques.
EMCA EMCA is a sulfhydryl-reactive (maleimide) compound to permanently cap protein or peptide cysteines with carboxyl groups (make caproic acid derivatives).
AEDP AEDP is an amine-and-carboxyl group containing compound that contains an internal disulfide bond; use with crosslinkers to modify functional groups on proteins and surfaces.
Traut's Reagent 2-Iminothiolane-HCl (CAS 4781-83-3) is an amine-reactive thiolation reagent to cap protein primary amines with sulfhydryl groups for immediate crosslinking.
Modification of the sulfhydryl group  NEM N-Ethylmalemide (NEM) is a small, sulfhydryl-reactive (maleimide) compound to permanently block the reduced cysteines of proteins or peptides to prevent disulfide bond formation.
MMTS Methyl methanethiosulfonate (MMTS) (CAS 2949-92-0) reversibly block cysteines (sulfhydryl groups) to help facilitate the study of enzyme activation and protein function.
EMCA EMCA is a sulfhydryl-reactive (maleimide) compound used to permanently cap protein or peptide cysteines with carboxyl groups (making caproic acid derivatives).
Other modification options  APTS 3-Aminopropyltriethoxysilane (APTS)is a silylation reagent for coating glass and silica surfaces to add primary amines, which can be used to crosslink and immobilize proteins and other molecules.
NaIO4 Sodium meta-periodate (NaIO4) (CAS 7790-28-5) is used to gently oxidize glycoprotein carbohydrate sugars to create reactive aldehydes (carbonyls) for crosslinking and immobilization.
 IAA Iodoacetic acid (IAA) is C2H3IO2 (CAS 64-69-7) is used to S-carboxymethylate sulfhydryls (reduced cysteines) at slightly alkaline pH for use in various protein biology methods.
Hydroxylamine-HCl Hydroxylamine-HCl (NbOH.HCl) (CAS 7803-49-8) is used to cleave Asn-Gly peptide bonds or to deprotect sulfhydryls following S-acetylthioacetate modification with SATA reagent.
GlycoLink Coupling Catalyst Aniline (CAS 62-53-3) and an optimized buffer is used to enhance aldehyde-hydrazide crosslinking efficiency for glycoprotein immobilization and conjugation.

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Protein quantitation immunoassays