The acidic pH of lysosomes is maintained by:
Lysosomes maintain a highly acidic lumen essential for optimal activity of about sixty acid hydrolases involved in macromolecular digestion and for solute transport. The steep proton gradient, pH 4.5 to 5.0 inside versus cytosolic pH 7.2, representing over two pH units and hundredfold proton concentration difference, is actively generated by vacuolar-type H+ ATPase, V-ATPase, consuming ATP. This massive multi-subunit rotary pump consists of peripheral V1 domain with A3B3 hexamer that hydrolyzes ATP and integral V0 domain forming proton channel with c-ring rotation. ATP hydrolysis drives rotati
Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 13: Lysosomes – V-ATPase and Acidification.