Mechanisms of loss of latency of lysosomal enzymes. Effects of incubation on the properties of lysosomal membranes

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Abstract
The effects of sucrose and KCl on the loss of latency of lysosomal enzymes caused by incubation at 37.degree. C, pH 7.4, were examined by using Triton-filled lysosomes from rat liver and 2 fractions from livers of rats not injected with Triton. After incubation, the percentage free activity of lysosomal enzymes was measured before and after cooling to 0.degree. C in order to determine the amount of latency lost at 37.degree. C without cooling and the additional amount lost on cooling the incubated lysosomes to 0.degree. C. The latency that is lost without cooling is first decreased and then increased by increasing the osmotic strength of the incubation medium with KCl, or with sucrose in the presence of KCl. If the osmotic strength is increased with sucrose alone, loss of latency is decreased up to 0.25 M sucrose, but is increased only slightly at higher sucrose concentrations. Apparently, the lysosome is permeated by hyperosmolar KCl but not by sucrose during incubation. If the osmotic strength of the assay medium is increased with KCl, the loss of latency caused by incubation for 60 min in hyperosmolar KCl is repressed. A KCl-permeated lysosome can evidently be obtained which is relatively stable until exposure to lower osmolarities. The loss of latency caused by cooling incubated lysosomes to 0.degree. C is largely eliminated if the osmotic strength of the medium in which the lysosomes are cooled is raised sufficiently with either sucrose or KCl. Osmotic-fragility curves were obtained after incubation for 1 and 60 min at isoosmoticity (0.2 M KCl or 0.25 M sucrose). Although little loss of latency occurs at isoosmoticity, lysosomes incubated for 60 min display greatly increased fragility on exposure to hypo-osmolar KCl, hypo-osmolar sucrose or hyperosmolar KCl. Permeability to KCl at 37.degree. C and the increase in fragility on exposure to hypo-osmolar conditions are probably both consequences of injury, probably from enzymic action, sustained by the lysosomal membrane during incubation at 37.degree. C.

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