Effect of pH in the acidic region on the structural integrity of lipase from wheat germ

To understand the structure-function relationship of the enzyme lipase the effect of acid pH on the activity of lipase has been followed using a number of physico-chemical techniques. Lipase from wheat/germ has S20,w value of 2.2 S and a molecular weight of 42,000 +/- 1,000. The enzyme has an intrinsic viscosity of 4.72 ml/g indicating it to be elongated in shape. With decrease in pH below 7.0 microenvironmental changes occur in the neighborhood of active site accompanied by minor conformational changes without any gross change in the hydrodynamic properties of the protein, as monitored with ultraviolet difference spectra, fluorescence spectra, viscosity and circular dichroism. The kinetics of the inactivation process has been established as consisting of a fast step and a slow step with a k value of 73/sec and 7.2/sec respectively. At extreme acid pH the enzyme reaggregates to a polymer arising out of hydrophobic interaction and the polymer has no activity.