Influence of urea on stability of invertase from Saccharomyces cerevisiae

Abstract

This paper aimed to investigate the dependence between the unfolding equilibrium of invertase by urea, according to a two-state mechanism, with the thermodynamic properties of the solvent as calculated by application of the McMillian-Mayer theory. Unfolding equilibrium of invertase was monitored by spectrophotometric titration at 280 nm with a 8 mol.L-1 urea solution, and compared with data for RNase A and RNase T1. The good fitting of the equilibrium data for all proteins using a first order model is consistent with the idea that the high carbohydrate content of invertase does not affect the general mechanism of protein unfolding. However, an increase in the urea concentration produced a decrease in the Gibbs free energy of unfolding (ï?„Gï‚°U) for invertase, and an increase in the ï?„Gï‚°U values for RNase A and RNase T1. Invertase also required higher water activity values (Aw) than RNAse A and RNAse T1 for unfolding. The different behavior of invertase in relation to those enzymes may be relevant to provide additional information about the detailed mechanisms of protein folding and unfolding.