Heat-stability of a proteinase from psychrotrophic Pseudomonas fluorescens P38, chymotrypsin and thermolysin

The heat-stabilities of proteinases from a psychrotrophic Psuedomonas fluorescens strain P38 (P38 proteinase), chymotypsin, succinyl-chymotrypsin and thermolysin are compared on the basis of their respective thermoinactivation-rate constants and Arrhenius plots (40–145°C). The Arrhenius plots for P38 proteinase and succinyl-chymotrypsin showed an inversion at 80–90°C characteristic of enzymes showing low-temperature inactivation (LTI). Thermolysin showed a biphasic log k versus 1/T plot consistent with the two-state model for protein and enzyme denaturation. The results are discussed in terms of the kinetics of proteinase autolysis and possible physico-chemical features necessary for LTI.