Heat inactivation of lipase from psychrotrophic Pseudomonas fluorescens P38: Activation parameters and enzyme stability at low or ultra-high temperatures

Abstract

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 ( ΔE #), enthalpy ( ΔH #), entropy ( ΔS #) and Gibbs free energy change ( ΔG #) for lipase inactivation at 40–140°C were determined. ΔH # for P38 lipase heat inactivation at 40–60°C, 50–80°C and 90–140°C was 170–221 kJ mol −1, −3 − −20 kJ mol –1 and 44–78 kJ mol −1 respectively. Over these temperature intervals ΔS # was 202–380 J mol −1 K −1, −318 − −375 J mol −1 K −1 and −92 − −186 J mol −1 K −1. ΔG # was 100–115 kJ mol −1 for enzyme inactivation at 40–140°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.