Evidence for the proximity of a cysteinyl and a tyrosyl residue in the active site of 6-phosphogluconate dehydrogenase

The treatment of 6-phosphogluconate dehydrogenase from Candida utilis with dansyl chloride causes the modification of one amino acid residue per enzyme subunit and the inactivation of the enzyme. Either a cysteine or a tyrosine residue can be modified, depending on the pH of the reaction mixture. The dansyl residue can be transferred from one residue to the other suggesting that the two amino acid residues are close in the tridimensional structure of the active site of the enzyme.