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#V-ATPase

2 public questions tagged with this topic.

Membrane Transportation

Which ATPase is involved in pH regulation in lysosomes and vacuoles?

V-class ATPases also called V-type vacuolar H+-ATPases are large multi-subunit rotary pumps related to F-type ATP synthases but functioning as ATP-driven proton pumps rather than ATP synthetic machines. Complex comprises peripheral V1 sector containing eight subunits including A3B3 hexamer that hydrolyzes ATP and membrane integral Vo sector with proteolipid c-ring, subunit a and accessory subunits mediating proton translocation. Hydrolysis-driven rotation of central stalk couples to c-ring rotation within Vo pumping H+ into lumen. In cells V-ATPase localizes to lysosomes, endosomes, vacuoles, Golgi, secretory vesicles and plasma membrane of intercalated cells, acidifying lumen to pH 4.5 to 5.5 required for activation of acid hydrolases, ligand-receptor dissociation, proprotein processing and secondary transport driven by H+ gradient. Inhibition by bafilomycin and concanamycin abolishes acidification, blocks lysosomal degradation and bone resorption by osteoclasts. Na+/K+ ATPase and CFTR do not mediate lysosomal acidification, highlighting V-type specialization for compartmental pH control. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.

Ref: Forgac, Nat Rev Mol Cell Biol 2007, Vacuolar H+-ATPases; Alberts, 7th ed., Chapter 13 acidification.

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Membrane Transportation

Which pump is responsible for maintaining low pH in lysosomes?

Lysosomes function as degradative centers requiring low internal pH between 4.5 and 5 to activate more than fifty acid hydrolases such as cathepsins, sulfatases and lipases, while protecting cytosol from unwanted proteolysis. Acidic environment established primarily by vacuolar proton ATPase V-ATPase, large 900 kilodalton complex composed of peripheral V1 octamer A3B3CDE3FG3H hydrolyzing ATP at A-B interfaces and integral Vo domain a, c, c'', d, e, forming proton pore. Mechanism rotary: ATP hydrolysis in V1 drives rotation of central stalk D F and c-ring proteolipid assembling ten copies each with essential glutamate protonating deprotonating at half channels in subunit a, transporting protons from cytosol to lumen consuming roughly four protons per ATP. No phosphoenzyme intermediate forms. Specific inhibitors bafilomycin and concanamycin bind Vo. Na+/K+ ATPase maintains plasma gradients, F-type ATP synthase in mitochondria normally synthesizes ATP using proton gradient, ABC transporters move organic molecules. Thus proton pumping and organelle acidification for low pH depends on V-class proton pump.

Ref: Forgac, Nature Reviews Mol Cell Biol, V-ATPase Structure and Lysosomal Acidification Function.

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