Abstract
The enzymes having G6PD activity were isolated from 10 species belonging to 8 invertebrate phyla and their properties were examined in order to compare with those of vertebrate G6PD and H6PD. As a result it has been demonstrated that invertebrate G6PD has properties quite similar to vertebrate G6PD in the following respects; (1) The primary substrates are G6P and NADP; (2) Km's for G6P and NADP are in the majority of cases of the order of 10-5M and 10-6M, respectively; (3) Mg ions have no or only a slight stimulative effect; (4) The molecular weight of the monomer is about 55×103 and the enzyme exists as a dimer and/or a tetramer.
No H6PD was found in the species studied.
From these and other data it may be speculated that animal G6PD would not have undergone a marked change in the substrate specificity and in the molecular weight of the monomer during evolution and that echinoderms might be the only one among invertebrates that possesses H6PD. This suggests that if G6PD and H6PD might have a common ancestral molecule, the divergence might have occurred at the time of echinoderm evolution.
