The Nature of the Amino Acid Residues Involved in the Inactivation of Gluconate 6-phosphate Dehydrogenase by Iodoacetate.

has been crystallized from Can&&z utilis (1). The kinetics (2) and the stereochemistry of the reaction (3) have been studied, but very little is known of the nature of the functional groups or amino acids involved in the catalysis. This report deals with the role of one or two sulfhydryl groups in the activity of the enzyme. Rapid inactivation has been found to take place upon treatment with iodoacetate, and complete inactivation has been achieved when 1.8 moles of iodoacetate are bound per mole of dehydrogenase. The alkylated amino acid has been identified as cysteine.