Effect of increasing concentrations of salt on the lysosomes of rat liver and Tetrahymena pyriformis

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

1. The effects of sucrose and KCl on the loss of latency of lysosomal enzymes caused by incubation at 37 degrees C, pH 7.4, were examined by using Triton-filled lysosomes from rat liver and two fractions from livers of rats not injected with Triton. 2. After incubation, the percentage free activity of lysosomal enzymes was measured before and after cooling to 0 degrees C in order to determine the amount of latency lost at 37 degrees C without cooling and the additional amount lost on cooling the incubated lysosomes to 0 degrees C. 3. 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. However, if the osmotic strength is increased with sucrose alone, loss of latency is decreased up to 0.25M-sucrose, but is increased only slightly at higher sucrose concentrations. Apparently the lysosome is permeated by hyperosmolar KCl but not by sucrose during incubation. 4. 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. Thus it appears that a KCl-permeated lysosome can be obtained which is relatively stable until exposure to lower osmolarities. 5. The loss of latency caused by cooling incubated lysosomes to 0 degrees 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. 6. Osmotic-fragility curves were obtained after incubation for 1 and 60 min at iso-osmoticity (0.2M-KCl or 0.25 M-sucrose). Although little loss of latency occurs at iso-osmoticity, lysosomes incubated for 60 min display greatly increased fragility on exposure to hypo-osmolar KCl, hypo-osmolar sucrose or hyperosmolar KCl. 7. It is suggested that permeability to KCl at 37 degrees C and the increase in fragility on exposure to hypo-osmolar conditions are both consequences of injury, probably from enzymic action, sustained by the lysosomal membrane during incubation at 37 degrees C.

Release and activation of a particulate bound acid phosphatase from Tetrahymena pyriformis

A sedimentable form of acid phosphatase (EC 3.1.3.2) from Tetrahymena pyriformis was found to be solubilized by Triton X-100. The total enzyme activity in the insoluble cell fraction increased almost 200% upon solubilization with Triton X-100 or Nonidet P-40. Removal of membrane lipids and Triton X-100 from the particulate wash solution with a chloroform extraction resulted in non-specific enzyme-protein aggregation which was reversible upon addition of Triton X-100. The results indicate that this acid phosphatase is an integral membrane protein. The pH optima for this particulate bound acid phosphatase was 3.5 with o-carboxyphenyl phosphate and 4.0 with p-nitrophenyl phosphate as substrates. The Km values of each substrate were 3.1 and 0.031 mM, respectively.

A thermally induced alteration in lysosome membranes: salt permeability at 0 and 37 degrees C

Preparations of radioactive lysosomes were obtained from mouse kidney after injection of radioactive iodine-labeled bovine ribonuclease. Stability of these lysosomes in various media was estimated from measurements of proteolytic activity towards the ribonuclease, and of ribonuclease retention in particles. The lysosomes were stable at 37 degrees C in isotonic, sucrose-free solutions of KCl, NaCl, and potassium acetate, and in mixtures of these with MgCl2, showing that these salts are relatively impermeant through the lysosomal membranes. The membranes were less permeable to Na+ than to K+. Both KCl and NaCl exerted their optimal protective effects over a broad concentration range above 0.125 M in 0.025 M acetate buffer. Mg2+ enhanced the protective effect of both K4 and Na+; the osmotic effect of 0.075 M NaC1-0.05 M MgCl2 was indistinguishable during the entire course of ribonuclease digestion from that of isotonic sucrose. Osmotic protection by KC1-MgC12 was demonstrated over the H range5.5-7.0. A marked alteration in membrane properties occurs at lower temperatures in 0.11 M KC1-0.01 M MgCl2 such that, at 0 degrees C, K+ permeability is much higher than at 37 degrees C, as shown by a several-fold decrease in stability at the lower temperature.