STRUCTURAL STABILITY OF LIPASE FROM WHEAT-GERM

Purified lipase from wheat germ was used for the determination of pref erential interaction parameters under different stabilizing cosolvent conditions. The partial specific volume of the enzyme was measured und er 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 (partial de rivative g(3)/partial derivative g(2))(T,mu 1,mu 3) 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 (partial derivative g(3) /partial derivative g(2))(T,mu 1,mu 3) 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 presenc e of these cosolvents by increasing its hydration, of which DMSO is st abilizing to the maximum extent. The stabilization of the enzyme was a lso confirmed by the thermal denaturation measurements in the presence of these cosolvents which indicated a shift in the apparent thermal d enaturation 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 o f the enzyme in the presence of these cosolvents. (C) Munksgaard 1994.