L-glutamate dehydrogenase from the Antarctic fish Chaenocephalus aceratus - Primary structure, function and thermodynamic characterisation: relationship with cold adaptation

In order to study the molecular mechanisms of enzyme cold adaptation, direc t amino acid sequence, catalytic features, thermal stability and thermodyna mics of the reaction and of heat inactivation of L-glutamate dehydrogenase (GDH) from the liver of the Antarctic fish Chaenocephalus aceratus (suborde r Notothenioidei, family Channichthyidae) were investigated. The enzyme sho ws dual coenzyme specificity, is inhibited by GTP and the forward reaction is activated by ADP and ATP. The complete primary structure of C. aceratus GDH has been established; it is the first amino acid sequence of a fish GDH to be described. In comparison with homologous mesophilic enzymes, the ami no acid substitutions suggest a less compact molecular structure with a red uced number of salt bridges. Functional characterisation indicates efficien t compensation of Q(10), achieved by increased k(cat) and modulation of S-0 .5, which produce a catalytic efficiency at low temperature very similar to that of bovine GDH at its physiological temperature. The structural and fu nctional characteristics are indicative of a high extent of protein flexibi lity. This property seems to find correspondence in the heat inactivation o f Antarctic and bovine enzymes, which are inactivated at very similar tempe rature, but with different thermodynamics. (C) 2000 Elsevier Science B.V. A ll rights reserved.