Alkaline serine proteinase from Thermomonospora fusca YX. Stability to heat and denaturants.

The serine proteinase isolated from Thermomonospora fusca YX shows considerable thermal stability up to 80 degrees C, and progressive inactivation occurs at higher temperatures. Lyotropic salts affected the thermal stability of the enzyme at 85 degrees C, suggesting that disruption of hydrophobic interactions play an important role in the decreased thermal stability of the enzyme above 80 degrees 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, Ca2+ binding does not appear to play a role in thermal stability. Denaturants, i.e. 8 M-urea, 6 M-guanidinium chloride or 1% SDS, had no significant effect on the activity of the enzyme after 24 h at 25 degrees C.