kinetic and thermodynamic properties of pseudomonas fluorescence lipase upon addition of sorbitol

Lipases, as an important enzyme group, are able to catalyze hydrolysis or synthesis of esters.The lipase from pseudomonas fluorescens (E.C.3.1.1.3) is a thermophilic kind of lipases (MW around 33 Kd).
In this study, the effect of different concentrations of sorbitol on the activity and conformational stability of Psedomonas fluorescence lipase was evaluated using UV/Vis and Circular Dichroism (CD), respectively. According to the results of thermodynamic studies the 0.6 M concentration of sorbitol was selected for refolding and unfolding kinetic measurements with stopped flow fluorescence apparatus. Kinetics data indicate that unfolding of lipase is performed via two different pathways; one of them is probably involves a synchronous unfolding and dissociation of subunits and the other one comprises a two step unfolding in which the subunits are first dissociated followed by complete unfolding of subunits. We found that more population of protein molecules unfolded with slow phase unfolding pathway when sorbitol is present in the unfolding buffer. Furthermore; refolding kinetics data suggest that in the presence of sorbitol the energy barrier of refolding is reduced.