|| Geisow MJ, D'Arcy Hart P, Young MR. Temporal changes of lysosome and phagosome pH during phagolysosome formation in macrophages: studies by fluorescence spectroscopy. J Cell Biol. 1981 Jun89(3):645-52.  Tycko B, Maxfield FR. Rapid acidification of endocytic vesicles containing alpha 2-macroglobulin. Cell. 1982 Mar28(3):643-51.  Coffey JW, De Duve C. Digestive activity of lysosomes. I. The digestion of proteins by extracts of rat liver lysosomes. J Biol Chem. 1968 Jun 25 243(12):3255-63  Ohkuma S, Poole B. Fluorescence probe measurement of the intralysosomal pH in living cells and the perturbation of pH by various agents. Proc Natl Acad Sci U S A. 1978 Jul75(7):3327-31.  Reeves, I. B. 1984. In Lysosomes in Biology and Pathology, ed. J. T. Dingle, R. T. Dean, W. Sly, pp. 175-199. Amsterdam: ElsevierPubMed ID6166620, 6176331, 5656369, 28524
||p.667 top paragraph: "The secondary lysosomes, the main intracellular digestive compartment,
constitute the terminal compartment of the pathway. With a pH of 4.5-5.0, the
lysosomes are the most acidic organelles in animal cell (primary sources 43-45)." p.672 bottom line:"A number of laboratories have shown that in intact cells, the intralysosomal environment is maintained at a pH of 4.6-5.0 (primary sources 9, 35, 43, 44)."