Lysosomes in Turnover and Modulation
A balanced discussion of the turnover of cells and of macromolecules under normal conditions, would take us far afield of our major topic and into questions of the regulation of macromolecule synthesis, cell division and so forth. Such broad ranging perspectives are reflected in some recent publications concerning turnover at one or another level of cell organization (see e.g., Cameron and Trasher 1971, Goldberg and Dice 1974, Poole 1971, Rechcigl 1971 a, Schimek 1973). We will restrict ourselves to degradative aspects of turnover and particularly to determining how lysosomes might fit in. One might expect lysosomes to play an essential role in turnover since these organelles represent the major intracellular sites of the known appropriate enzymes (Poole and De Duve 1973). This is not to imply that nonlysosomal enzymes are not at all involved. But the specificities of the few relevant non-lysosomal suspects, such as the dipeptidase that is present in the “cystol” fraction of cells (Barrett and Dingle 1971, Marks and Lajtha 1970, McDonald et al. 1971, Peters 1970) suggest that their roles are ancillary 10. Despite such considerations, direct demonstration of lysosomal participation in turnover has been possible chiefly for materials that function in extracellular locations and are destroyed through endocytosis. Even for these components we know much less than might be expected, especially about the mechanisms through which molecules come to be “selected” for destruction. And, the involvement of lysosomes in normal breakdown of intracellular materials is still a contentious matter.
KeywordsGolgi Apparatus Autophagic Vacuole Extracellular Material Acid Hydrolase Lysosomal Hydrolase
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