Structural stability of lipase from wheat germ

Purified lipase from wheat germ was used for the determination of preferential interaction parameters under different stabilizing cosolvent conditions. The partial specific volume of the enzyme was measured under both isomolal and isopotential conditions in phosphate buffer at pH 7.0, 0.02 M, and the value was found to be 0.730 +/- 0.001 and 0.731 +/- 0.002 mL/g, respectively. The partial specific volume measurements with different cosolvents indicated that the enzyme has a (delta g3/delta g2)T,mu1,mu3 values of -0.119 +/- 0.012, -0.073 +/- 0.009 and -0.141 +/- 0.020 g/g, respectively, in 25% glucose, 25% sucrose and 25% DMSO. The (delta g3/delta g2)T,mu1,mu3 values in 10 and 20% glycerol were -0.054 +/- 0.012 and -0.073 +/- 0.016 g/g, respectively. Based on these values it is clear that the enzyme is stabilized in the presence of these cosolvents by increasing its hydration, of which DMSO is stabilizing to the maximum extent. The stabilization of the enzyme was also confirmed by the thermal denaturation measurements in the presence of these cosolvents which indicated a shift in the apparent thermal denaturation temperature of the enzyme towards higher temperatures. The data are supported further by the ultraviolet difference spectral as well as fluorescence measurements in the presence of these cosolvents. The stabilization has been attributed to the preferential hydration of the enzyme in the presence of these cosolvents.