Alkaline serine proteinase from Thermomonospora

The serine proteinase isolated from Thermomonospora fusca YX shows considerable thermal stability up to 80 °C, and progressive inactivation occurs at higher temperatures. Lyotropic salts affected the thermal stability of the enzyme at 85 °C, suggesting that disruption of hydrophobic interactions play an important role in the decreased thermal stability of the enzyme above 80 'C. Thermal stability is highly pH-dependent; above pH 6.0-6.5 there is a sharp decrease in the stability of the enzyme, reflecting increased autolysis. Although some stabilization occurs upon increasing ionic strength, Ca2l binding does not appear to play a role in thermal stability. Denaturants, i.e. 8 M-urea, 6 M-guanidinium chloride or I % SDS, had no significant effect on the activity of the enzyme after 24 h at 25 'C.