Purification and properties of a lipolytic acyl-hydrolase from potato leaves

A lipolytic acyl-hydrolase was purified 520-fold from an homogenate of potato leaves (Solanum tuberosum L. cv. Benimaru). The purified enzyme showed a single protein band on polyacrylamide gel electrophoresis. The enzyme had an isoelectric point of 4.6 and a molecular weight of about 110,000. It had pH optima of 5.5 and 5.0, and Km values of 0.26 and 0.54 mM for monogalactosyldiacylglycerol and phosphatidylcholine, respectively. The pH dependences were altered by the addition of Triton X-100. No separation of these two hydrolyzing activities was achieved; the ratio of the specific activity of galactolipase to that of phospholipase (about 7/1) remained constant throughout the purification procedures. Both the activities were changed in parallel with each other by the addition of reagents and by heat treatment. The enzyme clearly catalyzed the deacylation of the several classes of galacto- and phospholipids. These results suggest that a single enzyme is responsible for both activities.