Enzymatic and functional heterogeneity of lysosomes

Applying various preparations methods regarded as optimal for histochemical localization of enzymes in unfixed tissues, the following concordant results were obtained after demonstration of acid phosphatase, beta-glucuronidase and acid-beta-galactosidase activities in rat livers sampled at four typical time-points of a 24h-period (10:00, 16:00, 22:00, 04:00). 1. The lysosomes revealed with these marker enzymes differ with respect to their location within the liver lobules, their average number, size and reactivity during the 24h-period. 2. Extralysosomal activities also vary depending on the time of day. This is a normal and cytogenetically explicable event and not the consequence of an inadequate technique, and argues for a dual localization of lysosomal enzymes in the cell. 3. The chemical heterogeneity of the lysosomes and extralysosomal enzymes is obviously an expression of functionally different populations of lysosomes. In addition to the differences in location and average number, the variations in activity do not occur synchronously, but are phase-shifted.