Practice question

V-class ATPases, vacuolar type H+-ATPases, are multi-protein rotary pumps distinct from glucose carriers SGLT or drug exporters ABCB1. They hydrolyze ATP in cytosolic V1 sector comprising A3B3 catalytic hexamer and use released energy to rotate central stalk and translocate protons through membrane-embedded Vo sector containing c-ring proteolipids and subunit a. Cellular localization includes lysosomes, endosomes, trans-Golgi network, synaptic vesicles, secretory granules, osteoclast ruffled border and kidney intercalated cell apical membrane. By acidifying compartments to pH 4.5-5.5 they create environment for acid hydrolase activation, protein processing, neurotransmitter loading via proton-coupled secondary transporters, and iron release from transferrin. In osteoclasts and kidney they pump H+ outward contributing to bone resorption and urine acidification. They do not transport glucose, which uses SGLT and GLUT families, nor export lipophilic drugs, which uses ABC transporters, and they are not restricted to bacteria but broadly expressed in eukaryotes for organellar pH regulation vital for autophagy and infection defense.