The distribution of phospholipase B in mammalian tissues.

The breakdown of phospholipids in animal tissues has for long been regarded as involving the removal of the fatty acid residues by the successive action of phospholipases A and B, followed, in lecithin breakdown, for example, by the degradation of the glycerylphosphorylcholine so formed by means of a specific diesterase. The initial removal of a single fatty acid from the phospholipid molecule results in the formation of a lysophosphatide. Because of the marked cytolytic properties of these compounds, together with the fact that lysolecithin has recently been shown to be present in lipid extracts of animal tissues (Marinetti, Witter & Stotz, 1957; Hadju, Weiss & Titus, 1957; Phillips, 1957, 1958), a comparison of the ability of different tissues to degrade the lysophosphatides by means of phospholipase B is of physiological interest. Although this enzyme was first recognized in rice bran by Contardi & Ercoli in 1933, and was found also to occur in certain moulds (Fairbairn, 1948) and bacteria (Hayaishi & Kornberg, 1954), little detailed work appears to have been done on its distribution in animal tissues. Noguchi (1944) studied a number of rabbit tissues, and found considerable phospholipase B activity in pancreas and lung. Shapiro (1953) obtained active preparations from glycerol extracts of ox pancreas, and Dawson (1956) has carried out a careful study of the properties of this enzyme in glycerol extracts of acetone-dried rat and sheep liver. Dawson also states that he obtained liberation of glycerylphosphorylcholine when glycerol extracts of rat kidney, spleen, brain and blood were incubated with lysolecithin, but no quantitative assessment of enzymic levels was given for these tissues. WVhile this paper was in preparation a comparison of some of the properties of the phospholipase B in rat intestinal mucosa with those of the lecithinase also present in this tissue has been published by Epstein & Shapiro (1959).