Identity and Activities of Lysosomal Enzymes in Parenchymal and Non‐Parenchymal Cells from Rat Liver

Abstract

1 Intact parenchymal and non-parenchymal cells were isolated from rat liver. The parenchymal cells were purified by differential centrifugation, while non-parenchymal cells were obtained free of parenchymal cell contamination by preferentially destroying the parenchymal cells with the aid of pronase (0.25%). 2 The ability to isolate pure intact parenchymal and non-parenchymal cells permitted the characterization and measurement of specific activities of various lysosomal enzymes, representing the main functional hydrolytic activities of the lysosomes in these distinct cell types. 3 Lysosomal enzymes catalysing the hydrolysis of the terminal carbohydrate moiety of glycoproteins and glycolipids were not particularly enriched in the non-parenchymal cells as compared to parenchymal cells. The ratio of the specific activities of non-parenchymal cells over parenchymal cells varied between 0.7 for N-acetyl-β-d-hexoseaminidase to 2.1 for α-glucosidase. This suggests no specific role of the non-parenchymal cells in the hydrolysis of terminal carbohydrate moieties of glycoproteins and glycolipids. 4 The enzymes acid phosphatase and aryl sulphatase, representing the phosphate and sulphate hydrolyzing activities, were enriched in the non-parenchymal cells as compared to the parenchymal cells by a factor of 2.5. 5 The most important peptidase cathepsin D, representing protein breakdown capacity, is enriched in the non-parenchymal cells as compared to parenchymal cells by a factor 6.0, suggesting a possible specific function of non-parenchymal cells in protein breakdown. 6 The most enriched lysosomal enzyme, representing lipid hydrolysis, is acid lipase, which is enriched in the non-parenchymal cells with a factor of 10. 7 The distribution of lysosomal enzymes between parenchymal and non-parenchymal cells suggests different functional roles of the lysosomes in these cell types. It can be concluded that the non-parenchymal cells possess a set of lysosomal enzymes which makes them extremely suitable for a phagocytic and antimicrobial function in the liver.