Evidence for the homology of hexose 6-phosphate dehydrogenase and glucose 6-phosphate dehydrogenase: comparison of the amino acid compositions.

Amino acid compositions of hexose 6-phosphate dehydrogenase and glucose 6-phosphate dehydrogenase from crucian carp and rat, and that of sea-urchin glucose 6-phosphate dehydrogenase were compared in order to ascertain if they are homologous enzymes. The results demonstrated that the overall amino acid compositions of the two enzymes remarkably resemble each other, and that the composition divergence (D = 0.038) of the crucian carp enzymes is in the range of those for homologous proteins so far reported. These findings strongly support our previous prediction that the two enzymes have diverged from a common ancestral molecule.