Comparative studies on thermophilicity and thermostability of aspartate aminotransferases.

Aspartate aminotransferase from Sulfolobus solfataricus (AspATSs) is an extremely thermophilic and thermostable enzyme. In order to investigate the structural features which underlie thermophilicity and thermostability, two isoforms of AspATSs differing by a single amino acid residue were compared. The first isoform is the naturally occurring enzyme, whereas the second is a genetically engineered mutant. Thermophilicity, short-term and long-term thermostability of the isoenzymes were independently evaluated and the influence of a cysteine residue on the three properties was assessed.