The Lysosomal Proton Pump
Acid assists digestion. That this is true at the subcellular as well as the organismal level was recognized more than 90 years ago by Metchnikoff (1893), who observed that blue litmus turned red when engulfed by protozoans. Today it is universally recognized that lysosomes, the intracellular digestive organelles, show an internal pH approximately 2 units below that of their environment. This not only provides favorable conditions for the activity of lysosomal enzymes, which have acidic pH optima, but also assists directly in the digestive process by denaturing ingested proteins to make them more susceptible to enzymatic proteolysis. In other organelles, internal acidification serves a variety of more subtle purposes. The dissociation of ligands from their receptors in endosomes, the accumulation of catecholamines in storage granules, and the processing and sorting of newly synthesized proteins in the Golgi are processes that are regulated in part by intraorganellar acidity. The transmembrane pH gradient in these organelles is generated and maintained by an ATP-dependent proton pump residing in the organellar membrane. This chapter summarizes the evidence for, and the characteristics of, the proton pump found in lysosomes.
KeywordsProton Pump Acridine Orange Acridine Orange Aryl Sulfatase Chromaffin Granule
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- Maunsbach, A., 1969, Functions of lysosomes in kidney cells, in: Lysosomes in Biology and Pathology, Vol. 1 (J. T. Dingle and H. R. Fell, eds.), North-Holland, Amsterdam, pp. 115–153.Google Scholar
- Metchnikoff, E., 1983, Lectures on the Comparative Pathology of Inflammation, Kegan, Paul, Trench, Trübner and Co., London.Google Scholar
- Reeves, J. P., 1984, The mechanism of lysosomal acidification, in: Lysosomes in Biology and Pathology, Vol. 7 (J. T. Dingle, R. T., Dean, and W. Sly, eds.), Elsevier, Amsterdam, pp. 175–199.Google Scholar