How do lysosomes maintain their pH?

Lysosomes have an acidic interior pH of ~4.8 compared to the slightly basic cytosol (pH 7.2). This pH differential is maintained by pumping in protons from the cytosol across the membrane via proton pumps and chloride ion channels. Lysosomes are known to contain more than 60 different enzymes, and this acidic pH is essential to the optimal activity of these hydrolytic enzymes.

The lysosomal membrane is an important boundary of the organelle. It confines the pH-sensitive hydrolytic enzymes within the lysosome, and protects the cytosol and the rest of the cell from these degradative enzymes. Since these enzymes are pH-sensitive and do not function well or at all in the alkaline environment of the cytosol, cytosolic molecules and organelles are ensured not to be destroyed in case there is leakage of the hydrolytic enzymes from the lysosome.