Molecular diversity of glucose-6-phosphate dehydrogenase: rat enzyme structure identifies NH2-terminal segment, shows initiation from sites nonequivalent in different organisms, and establishes otherwise extensive sequence conservation.

The NH2-terminal region of rat liver glucose-6-phosphate dehydrogenase (EC 1.1.1.49) is shown to differ radically from a reported amino acid sequence for the fruit fly enzyme and from one for the human enzyme. The results indicate considerable differences in the translational start point. However, a close relationship with another reported sequence for the human enzyme is established, now showing agreement between an indirectly deduced and a directly analyzed NH2-terminal structure of this enzyme type. The results provide evidence of one structural motif common to mammalian species but also suggest that genetic inconstancy 5' to, or at the start of, the region coding for the enzyme protein could be a source of intra- and interspecies diversity. This is of interest in relation to the large number of genetic variants of human glucose-6-phosphate dehydrogenase.