Enzymes in antarctic fish: glucose-6-phosphate dehydrogenase and glutamate dehydrogenase.

Glucose-6-phosphate dehydrogenase (G6PD) and L-glutamate dehydrogenase (GDH) from Antarctic fish were isolated and characterized. G6PD was purified from the erythrocytes of red-blooded Dissostichus mawsoni and from the colorless blood of the icefish Chionodraco hamatus. Structural and functional characterization showed that the two enzymes do not differ significantly from each other. GDH was purified from the liver of the icefish Chaenocephalus aceratus. As in other fish ODHs, it showed a marked preference for NAD-. The amino acid sequence of the active-site peptide is virtually identical to that of other fish and vertebrate counterparts. Although the basic structural features of the Antarctic enzymes are similar to those of mesophilic organisms, some catalytic and thermodynamic properties make the Antarctic enzymes more suited to cold-adapted organisms.