Mechanisms of heat inactivation of a proteinase from Pseudomonas fluorescens biotype I.

Heat inactivation of a metalloproteinase, isolated from Pseudomonas fluorescens biotype I strain 112, was investigated in the temperature ranges 50-60 degrees C and 90-140 degrees C. At 90 degrees C the denaturation of the enzyme followed first-order kinetics with a decimal reduction time of 110 min and a velocity constant K of 3.5 X 10(-4) S-1. Activation energy Ea was 100 kJ/mol for this temperature range. In the 50-60 degrees C region the proteinase was inactivated by autolysis, as shown by electrophoresis and gel filtration. At 55 degrees C the decimal reduction time was approximately 22 s, at 57 degrees C it was 8 s. Rapid inactivation at 55 degrees C was only possible if the enzyme was heated from lower temperatures, but not if cooled down from 90 degrees C. This is due to a conformational change of the protein at this temperature. A model for the description of heat inactivation in the two temperature ranges is proposed.