Sensitivity to vanadate and isoforms of subunits A and B distinguish the osteoclast proton pump from other vacuolar H+ ATPases.
Analysis of proton (H+) transport by inside-out vesicles derived from highly purified chicken osteoclast (OC) membranes has revealed the presence of a newly discovered type of vacuolar H+ ATPase (V-ATPase). Unlike vesicles derived from any other cell type or organelle, H+ transport in OC-derived vesicles is sensitive to V-ATPase inhibitors (N-ethylmaleimide and Bafilomycin A1) and vanadate (IC50, 100 microM), an inhibitor previously found to affect only P-type ATPases. The OC H+ ATPase contains several V-like subunits (115, 39, and 16 kDa) but subunits A and B of the catalytic domain of the enzyme differ from that of other V-ATPases. In OCs, subunit A has a mass of 63 kDa instead of the 67-70 kDa expressed in monocytes, macrophages, and kidney microsomes, which contain a vanadate-insensitive H+ ATPase. Moreover, two types of 57- to 60-kDa B subunits are also found: one is expressed predominantly in OCs and the other is expressed in kidney microsomes. The OC H+ pump may therefore constitute a class of H+ ATPase with a unique pharmacology and specific isoforms of two subunits in the catalytic portion of the enzyme. This H+ ATPase is involved in resorption of bone and may be expressed in a cell-specific manner, thereby opening possibilities for therapeutic intervention.
Chatterjee
D
D
Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510.
Chakraborty
M
M
Leit
M
M
Neff
L
L
Jamsa-Kellokumpu
S
S
Fuchs
R
R
Baron
R
R
D000818:Animals; D001693:Biological Transport, Active; D002645:Chickens; D002837:Chromaffin Granules / Q000201:enzymology; D005033:Ethylmaleimide / Q000494:pharmacology; D005260:Female; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000737:chemistry; D008970:Molecular Weight; D010010:Osteoclasts / Q000201:enzymology*; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors* / Q000737:chemistry; D014617:Vacuoles / Q000201:enzymology; D014638:Vanadates / Q000494:pharmacology*
D007527:Isoenzymes; D014638:Vanadates; D006180:Proton-Translocating ATPases; D005033:Ethylmaleimide