Human liver was homogenised and fractionated by differential centrifugation, and the subcellular fractions were characterised biochemically. Absolute values and distribution patterns of protein and marker enzyme activities obtained from human liver have also been compared with those from rat liver. In addition, acid phospholipase activities have been studied in human liver. On the basis of product formation from stereo-specifically radiolabeled phosphatidylethanolamine substrates, lysosomal phospholipases A1 and A2 with optimal activities at pH 4.7 have been identified in human liver. Acid phospholipase C and lysophospholipase activities, however, were not found in human liver. Cationic amphiphilic drugs inhibited the activities of the acid phospholipases A in human and rat liver lysosomes to about the same extent.
