Thermophilic Alanine Dehydrogenase from <i>Halobacterium salinarium</i>

Abstract

Alanine dehydrogenase (L-alanine:NAD + oxidoreductase (deaminating), EC 1.4.1.1) from Halobacterium salinarium requires high concentrations of NaCl for both activity and stability. The enzyme is thermophilic with an optimum temperature of 70 °C in 3.4 M KCl and of 60 °C in 3.4 M NaCl. A thermophilic character has also been found for six other enzymes from H. salinarium. The alanine dehydrogenase becomes inactivated if the NaCl concentration drops below 1.5 M and it becomes reactivated if the salt concentration is increased to 4 M. Both reactions, the inactivation as well as the reactivation, require the presence of 2-mercaptoethanol for a complete reactivation. The reactivation reaction is irreversibly inhibited by N-ethylmaleimide.