Intracellular digestion of endocytosed proteins as a source of amino acids for protein synthesis in Trypanosoma cruzi.

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The discovery of lysospmes, with their semipermeable membranes and formidable battery of proteolytic enzymes, gave coherence to long-standing data on the pinocytic uptake of proteins by cells. Largely through the work of Werner Straus in the early 1960s, it became clear that most cells appear to have the capacity to internalize soluble extracellular proteins by either fluid phase or adsorptive pinocytosis (Silverstein et al., 1977). In most cases, the terminal events are that pinocytic vesicles migrate inward and fuse with lysosomes, so that pinocytosed proteins, and by inference other macromolecules, find themselves in contact with lysosomal enzymes within a “digestive vacuole” or “secondary lysosome” (de Duve and Wattiaux, 1966). Since the lysosomal enzymes are able to digest proteins to amino acids and dipeptides (Coffey and de Duve, 1968) and the membrane of the secondary lysosome is impermeable to peptides above molecular weight 220 Da (Ehrenreich and Cohn, 1969), it could be concluded that exogenous proteins would be retained within the vacuole until digestion was essentially complete and that the digestion products would then be transported into the cytoplasm for further catabolism or to be used for protein synthesis. This process of salvaging the cell’s “building blocks” is a primary nutritional function of lysosomes. Specific lysosomal transport systems for cystine, the cationic amino acids, small neutral amino acids, and large neutral amino acids have been recently described (Gahl, 1989).KeywordsEssential Amino AcidTrypanosoma CruziMouse Peritoneal MacrophageTrypanosoma BruceiExogenous ProteinThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.