Glutamate dehydrogenase from two Antarctic organisms, the icefish Chaenocephalus aceratus and the bacterium Psychrobacter sp TAD1

Glutamate dehydrogenase (GDH) was purified from the liver of the teleost Ch aenocephalus aceratus (Notothenioidei: Channichthyidae) and the microorgani sm Psychrobacter sp. TAD1, from Antarctic marine and terrestrial environmen ts, respectively. GDH isolated from C. aceratus liver had a hexameric molec ular structure very similar to that of other vertebrates and displayed pref erence for NAD(+), a feature shared with other fish enzymes. The bovine and fish GDH activity and stability were differently affected by temperature a nd hydrostatic pressure. At low temperatures, the specific activity of fish GDH was higher than that measured with the homologous bovine enzyme. Psych robacter sp. TAD1 showed a feature quite unusual in bacteria, i.e. the pres ence of two distinct GDHs specific either for NADP(+) or for NAD(+). NADP() -dependent GDH was purified and characterised. It has a hexameric structu re with a subunit molecular weight similar to that described for this class of GDHs and a specific activity at low and moderate temperatures similar t o that measured with the homologous enzyme from Escherichia coli. The kinet ic properties of NADP(+) -dependent GDH of Psychrobacter sp. TAD1 and the p resence of another NAD(+)-dependent GDH suggest that, during the cold-adapt ation process, this enzymatic function acquired a pattern of changes differ ent from that of C. aceratus.