Heterogeneity of lysosomes originating from rat liver parenchymal cells. Metabolic relationship of subpopulations separated by density-gradient centrifugation

Abstract

A crude lysosomal fraction obtained by differential centrifugation of a rat liver homogenate was subjected to zonal centrifugation in iso-osmotic self-generating gradients composed of modified colloidal silica (Percoll). Analysis of relevant marker-enzyme activities shows a continuous band of considerably purified lysosomal particles in the density range 1.04-1.11 g/ml. A relationship between age and buoyant density of the parenchymal lysosomal subpopulations is indicated by the distribution of 125I-labeled asialoglycoproteins in the heterogeneous lysosomes during the catabolism of the glycoprotein. The labeled asialoglycoprotein 1st appeared in lysosomal particles of low density, which with time progressively acquired a higher density. Thirty min after administration the 125I-labeled asialoceruloplasmin recovered in the light lysosomes was less degraded than the material recovered in the heavy lysosomes. A lysosomal enzyme (arylsulfatase) was found to possess considerably higher isoelectric points in the heavy lysosomes than in the light lysosomes, which is consistent with a relationship between age and density of the lysosomes.