A comparative study of invertebrate glucose 6-phosphate dehydrogenases.

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Abstract
The enzymes having G6PD [glucose-6-phosphate dehydrogenase] activity were isolated from 10 spp. [sponge, Haliclona permollis; hydra, Palmatohydra robusta; sea anemone, Epiactis japonica; sipunculid, Physcosoma yezoense; planarian, Dugesia japonica; ascarid, Ascaris lumbricoides; scallop, Patinopecten yessoensis squid, Ommastrephes sloani pacificus; earthworm, Pheretima hilgendorfi; crayfish, Procambarus clarki.] belonging to 8 invertebrate phyla and their properties were examined in order to compare with those of vertebrate G6PD and H6PD [hexose-6-phosphate dehydrogenase]. Invertebrate G6PD has properties quite similar to vertebrate G6PD in the following respects. The primary substrates are G6P and NADP. Km for G6P and NADP are in the majority of cases of the order of 10-5 M and 10-6 M, respectively. Mg2+ have no or only a slight stimulative effect. The MW of the monomer is about 55 .times. 103 and the enzyme exists as a dimer and/or a tetramer. No H6PD was found in the species studied. Animal G6PD would not have undergone a marked change in the substrate specificity and in the MW of the monomer during evolution and echinoderms might be the only ones among invertebrates that processes H6PD. If G6PD and H6PD might have a common ancestral molecule, the divergence might have occurred at the time of echinoderm evolution.