Incorporation of L-[35S]cysteine into rabbit muscle glyceraldehyde-3-phosphate dehydrogenase was detected following incubation of the enzyme in a mixture containing glyceraldehyde-3-phosphate, NAD+ and the labeled cysteine. Insignificant binding occurred in the absence of either the substrate or NAD+, suggesting that formation of an acylated enzyme form was a prerequisite for the binding. Stoichiometry of the binding depended on the number of functioning active centers; up to 4 moles of L-[35S]cysteine bound per mole tetramer with fresh enzyme preparations. The L-[35S]cysteine incorporation depended on pH and was maximal when a group having pKa of 8.5 is protonated. To clarify the relevance of this finding to the effect of SH-containing compounds previously shown to decrease the rate of 3-phosphoglyceroyl-enzyme hydrolysis [Kuzminskaya et al., FEBS Lett. 336 (1993) 208-210], the pH-dependence of the effect of glutathione on the hydrolysis rate was determined and found to be close to the pH-dependence of L-[35S]cysteine binding.