HEAT INACTIVATION OF LIPASE FROM PSYCHROTROPHIC PSEUDOMONAS-FLUORESCENS P38 - ACTIVATION PARAMETERS AND ENZYME STABILITY AT LOW OR ULTRA-HIGH TEMPERATURES

A quantitative model is presented for the heat inactivation of enzymes at low or ultra-high temperatures. As a test of its validity, the heat inactivation of crude or partially purified lipase from Pseudomonas fluorescens, strain P38 (P38 lipase) was investigated. The activation energy (DELTA-E#), enthalpy (DELTA-H#), entropy (DELTA-S#) and Gibbs free energy change (DELTA-G#) for lipase inactivation at 40-140-degrees-C were determined. DELTA-H# for P38 lipase heat inactivation at 40-60-degrees-C, 50-80-degrees-C and 90-140-degrees-C was 170-221 kJ mol-1, -3 - -20 kJ mol-1 and 44-78 kJ mol-1 respectively. Over these temperature intervals DELTA-S# was 202-380 J mol-1 K-1, -318-375 J mol-1 K-1 and -92 - -186 J mol-1 K-1. DELTA-G# was 100-115 kJ mol-1 for enzyme inactivation at 40-140-degrees-C. The results are consistent with different rate-limiting reactions for P38 lipase heat inactivation at low or ultra-high temperatures. Within a narrow range of (intermediate) temperature, a third rate-limiting reaction may lead to 'low-temperature inactivation' phenomena. There was qualitative agreement between experimental results and the current model for enzyme heat inactivation.