The role of lysosomal enzymes in protein degradation in different types of rat liver cells.

Highly purified suspensions of parenchymal, endothelial and Kupffer cells were prepared from the rat liver. The respective roles of these cell classes in the degradation of proteins was investigated by analysing the cellular distribution of two lysomal proteases. The specific arginine naphthylamidase activity was 2 times higher in Kupffer cells compared with the nearly equal activities in endothelial and parenchymal cells. The specific activity of the important endopeptidase cathepsin D in endothelial and Kupffer cells was about 12 and 36 times higher, respectively, than the activity in parenchymal cells. These results are in agreement with an important role of Kupffer and endothelial cells in the degradation of proteins and protein containing material of exogenous origin.