Thermopsin, A Thermostable Acid Protease from Sulfolobus Acidocaldarius

Abstract

Most of the well-studied aspartic proteases, including those derived from yeast, fungi, plants and animal sources, are stable in temperatures up to about 50° to 60°C. Aspartic proteases which can function at high temperature in the range of 80° to 100°C have not been reported so far. We searched for thermostable acid proteases in the thermoacidophilic archaebacteria, Sulfolobus acidocaldarius, Sulfolobus solfataricus, and Thermoplasma acidophilum, because these organisms grow best in acidic media in a pH near 2 and at temperature of 80°C. Using a highly sensitive radioassay (Lin et al, 1989), we found proteolytic activities in the cultures of all three bacteria. The highest activity was found in Sulfolobus acidocaldarius. This protease was named thermopsin.