“…In the first place a membranous enzyme activated by Ca 2+ may regulate entry of material into the lysosome. In view of the widely observed stimulation of fusion by Ca 2+ [7,25,28,30,32,33,34,38,47,48] one can consider the possibility that the ATPase regulates the free Ca 2+ concentration, e.g., by pumping Ca 2+ into the lysosome. Thus the ATPase may function in the membrane fusion process by means of which material from endocytotic vesicles and autophagic vacuoles is taken into lysosomes for digestion.…”