Studies on lysophospholipases. IV. The subcellular distribution of two lysolecithin-hydrolyzing enzymes in beef liver

1. In a previous paper (Biochim. Biophys. Acta (1974) 369, 50-63) the purification of two proteins with lysophospholipase activity (EC 3.1.1.5), provisionally denoted lysophospholipase I and lysophospholipase II, has been described. The subcellular localization of both enzymes was investigated by cell fractionation studies. 2. For each subcellular fraction the total lysophospholipase activity, after solubilization by n-butanol treatment, was separated into a lysophospholipase I and II contribution by DEAE-Sephadex ion exchange chromatography. 3. Lysophospholipase I was found to be a soluble enzyme with a bimodal distribution. Highest relative specific activities were measured in the mitochondrial and the cytoplasmic fraction. Evidence is presented indicating that this enzyme is present in the mitochondrial matrix fraction. 4. Lysophospholipase II appeared to be a membrane-bound enzyme with highest relative specific activity in the microsomal fraction.