Abstract
An intracellular aminopeptidase (EC 3.4.11.-) was purified from the extreme thermophilic archaebacterium, Sulfolobus solfataricus. The molecular weight of the native enzyme was about 320 000, as calculated by gel-filtration studies, and subunit M r of 80 000 was estimated by SDS-polyacrylamide gel electrophoresis. The temperature optimum of the enzyme was at 75°C and the pH optimum was found to be 6.5. Th e aminopeptidase was highly active against the chromogenic substrates l-Leu-p-DNA and l-Ala-p-DNA. The enzyme was inhibited by EDTA, but the activity could be partially restored by removal of the EDTA and incubation with Co 2+ or Mn 2+. Bestatin, a typical inhibitor of aminopeptidase, fully inhibited the enzyme activity, but inhibitors of serine proteinases had no effect. Beside a high thermostability, the enzyme showed a remarkable stability against 6 M urea, organic solvents and acetonitrile.
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