Evidence for the proximity of a cysteine and a lysine residue in the active site of 6-phosphogluconate dehydrogenase from Candida utilis

The environment of a cysteine residue in the active site of 6-phosphogluconate dehydrogenase from Candida utilis was investigated by means of N-(3-pyrene) maleimide. The reaction between enzyme and inhibitor results in the modification of one cysteine residue per enzyme subunit, and in the complete inactivation of the enzyme. In a second step, the epsilon-amino group of a lysine residue causes an intramolecular aminolysis of the bound inhibitor. These results indicate that a lysine and a cysteine residues are close in the three-dimensional structure of the active site of 6-phosphogluconate dehydrogenase.