Functionally important regions of glucose-6-phosphate dehydrogenase defined by the Saccharomyces cerevisiae enzyme and its differences from the mammalian and insect forms.

The primary structure of Saccharomyces cerevisiae glucose-6-phosphate dehydrogenase has been determined. It consists of 503 amino acid residues, with an acetyl-blocked N-terminus. The structure shows equally extensive differences from the corresponding mammalian and fruit fly enzymes (52% residues non-identical). Residues conserved in all the forms constitute about 40% of the structures and include two histidines. One of these (His200 in the numbering of the rat enzyme) occurs in a 10-residue conserved segment, including the reactive Lys204, probably related to substrate binding. Two segments with conserved Gly-Xaa-Xaa-Gly-Xaa-Xaa-Gly/Ala pattern constitute possibilities for the coenzyme-binding site. One is N-terminally located (positions 37-43) with two conserved arginine residues nearby (positions 56 and 71), of interest for phosphate binding. The other (positions 241-247) is in a middle region, with many residue identities, containing the conserved residues Arg256 and His264.