Other Notes Sulfhydryl reagent1,2 Application Reagent for the modification of cysteine residues in proteins. Used in protein sequencing (including by Sanger in sequencing bovine insulin) to prevent oxidation of -SH sidechains. Reagent for the modification of cysteine residues in proteins. Used to induce animal osteoarthritis model system, which mimics both symptoms and histopathology of the human disease.