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A histochemical and biochemical analysis of lysosomes in Sarcoma 180 ascites tumor cells
Electron microscope histochemical and biochemical properties of S 180 lysosomes were studied in terms of intracellular disposition and stability. Using acid phosphatase and 5’ nucleotidase localization procedures, dense body lysosomes, secondary lysosomes, residual bodies and unusually large, lipoidal lysosomes were identified at the cell periphery. Electron micrographs reveal that these structures are continually passed from the cell to the exterior; a finding which possibly explains the general paucity of lysosomes in tumor cells. In spite of this small population of lysosomes, biochemical assays demonstrate high levels of lysosomal enzyme activity within these cells. Moreover, similar high levels of activity are found in the peritoneal fluid of the in vivo system as well as in the in vitro system where cells are grown in culture for up to 72 hours. Acid phosphatase with a high latency factor, is released into the extracellular environment at a low rate and remains unchanged over a period of three days. Cathepsin D has a high latency and is more active though more erratic extracellularly than acid phosphatase. Cathepsin B-1 has no latency, but when it is not inhibited by a serum factor, it shows a far greater level of extracellular activity than cathepsin D. Cathepsin B-1 is quite effective at ‘near’ neutral pH and attacks proteins quickly. Thus, this enzyme in particular is implicated in the many structural changes which occur at tumor cell surfaces. However, the possibility that other neutral lysosomal proteases contribute to cell surface protein degradation is not discounted.