Journal of Lipid Research, Vol. 8, 479-485, September 1967
Copyright © 1967 by Lipid Research, Inc.

Hydrolysis of phospholipids by a lysosomal enzyme

A. Mellors and A. L. Tappel

Department of Food Science and Technology, University of California, Davis, California 95616

The phospholipid-hydrolyzing activity of rat liver lysosomes has been studied. These lysosomes contain a phospholipase that cleaves both fatty acid ester linkages of lecithin and of phosphatidyl ethanolamine and releases free fatty acids from both positional isomers of lysolecithin. The enzyme does not require calcium for maximum activity, and is inhibited by diethyl ether and sodium deoxycholate. Mercuric ions and cetyltrimethyl ammonium bromide also inhibit the hydrolysis. Compared with lipase activity, this enzyme is relatively stable to heat.

The specific activity of the hydrolysis of lecithin by the lysosomal enzyme is considerably higher than those reported for mitochondrial and microsomal phospholipases. The enzyme resembles other hydrolases of the lysosome in that it has an acid pH optimum (pH 4.5). This enzymic activity is present in both the lysosomal soluble enzyme fraction and in the lysosomal membrane fraction.

The enzyme may participate in the intracellular digestion of mitochondria that is carried out by the intact lysosome in vivo. Localized inflammation and changes in vascular permeability following tissue damage could be catalyzed by this phospholipase.

Supplementary key words lysosomes • rat liver • phospholipase • lecithin • phosphatidyl ethanolamine • lysolecithin • phospholipid • mitochondria • uncoupling • inflammation

Submitted on March 15, 1967
Accepted on May 18, 1967

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