BROMOPYRUVATE FOR THE AFFINITY LABELING OF A SINGLE CYSTEINE RESIDUE NEAR THE CARBOXYLATE BINDING-SITE OF LAMB LIVER 6-PHOSPHOGLUCONATE DEHYDROGENASE

Bromopyruvate inactivates 6-phosphogluconate dehydrogenase by affinity labeling. Kinetic analyses, stoichiometry and isolation of a single l abelled tryptic peptide of the modified protein indicate that inactiva tion is due to the affinity labeling of a single cysteine residue, ide ntified as cysteine 401. It thus appears that this cysteine is within a short distance from the protein site involved in the binding of the carboxylate group of the substrate. These results suggest that the car boxylate binding site of proteins could be used as an anchorage point for affinity labeling, and that bromopyruvate can be used to individua te an amino acid residue within few A from this site.