The conformational stability of a lipase from a psychrotrophic Pseudomonas fluorescens

The reversible unfolding by heat or guanidine hydrochloride of lipase from a psychrotrophic Pseudomonas fluorescens was studied by fluorescence spectrophotometry. Lipase conformational stability was assessed based on thermodynamic parameters, e.g. free energy (ΔG), enthalpy (ΔH), entropy (ΔS) and heat capacity (ΔCp) changes for unfolding. The degree of reversibility was 70% and 100% for heat or guanidine hydrochloride unfolding. ΔG(25°C), ΔG(H2O), ΔHm, ΔSm and ΔCp values for lipase unfolding were 9.5, 6.5 and 151 kJ/mol, 475 J/mol/K and 4.06 kJ/mol/K respectively. The ΔG values determined by direct monitoring of unfolding were comparable to the value of 15 kJ/mol estimated from the enzyme temperature-activity profile. The conformational stability of lipase from the psychrotrophic Pseudomonas fluorescens is shown to be significantly lower than the stability usually observed for mesophilic enzymes.