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 Chaenocephalus aceratus (Notothenioidei: Channichthyidae) and the microorganism Psychrobacter sp. TAD1, from Antarctic marine and terrestrial environments, respectively. GDH isolated from C. aceratus liver had a hexameric molecular structure very similar to that of other vertebrates and displayed preference for NAD+, a feature shared with other fish enzymes. The bovine and fish GDH activity and stability were differently affected by temperature and hydrostatic pressure. At low temperatures, the specific activity of fish GDH was higher than that measured with the homologous bovine enzyme. Psychrobacter sp. TAD1 showed a feature quite unusual in bacteria, i.e. the presence of two distinct GDHs specific either for NADP+ or for NAD+. NADP+ -dependent GDH was purified and characterised. It has a hexameric structure with a subunit molecular weight similar to that described for this class of GDHs and a specific activity at low and moderate temperatures similar to that measured with the homologous enzyme from Escherichia coli. The kinetic properties of NADP+ -dependent GDH of Psychrobacter sp. TAD1 and the presence of another NAD+-dependent GDH suggest that, during the cold-adaptation process, this enzymatic function acquired a pattern of changes different from that of C. aceratus.