Amino acid sequence of ovine 6-phosphogluconate dehydrogenase.

The amino acid sequence of the NADP+-dependent enzyme ovine 6-phosphogluconate dehydrogenase has been determined by conventional direct protein sequence analysis of peptides resulting from digestion of the protein with trypsin and chemical cleavages with cyanogen bromide, hydroxylamine, and iodosobenzoic acid. The polypeptide contains 466 amino acids and its NH2 terminus is acetylated. The Candida utilis enzyme is inactivated by reaction of pyridoxal phosphate with two lysine residues (Minchiotti, L., Ronchi, S., and Rippa, M. (1981) Biochim. Biophys. Acta 657, 232-242). These residues are conserved in the ovine enzyme. In contrast to NAD+ dehydrogenases which have weakly related sequences and spatially related folds in their nucleotide-binding sites, no significant sequence homologies were detected between 6-phosphogluconate dehydrogenase and any of three other NADP+-requiring enzymes, glutamate dehydrogenase, p-hydroxybenzoate hydroxylase, and dihydrofolate reductase. This is in accord with structural data that show no spatial relationship between NADP+-binding sites in these enzymes.