title: Purification and properties of a vanadate- and N-ethylmaleimide-sensitive ATPase from chromaffin granule membranes.
abstract: A vanadate- and N-ethylmaleimide-sensitive ATPase was purified about 500-fold from chromaffin granule membranes. The purified preparation contained a single major polypeptide with an apparent molecular mass of about 115 kDa, which was copurified with the ATPase activity. Immunological studies revealed that this polypeptide has no relation to subunit I (115 kDa) of the H+-ATPase from chromaffin granules. The ATPase activity of the enzyme is inhibited about 50% by 100 microM N-ethylmaleimide or 5 microM vanadate. The enzyme is not sensitive to dicyclohexylcarbodiimide, ouabain, SCH28080, and omeprazole, which distinguishes it from Na+/K+-ATPase and the gastric K+/H+-ATPase. ATP and 2-deoxy ATP are equally effective substrates for the enzyme. However, the enzyme exhibited only 10% activity with GTP as a substrate. UV illumination of the purified enzyme in the presence of [alpha-32P]ATP exclusively labeled the 115 kDa protein. This labeling was increased by Mg2+ and strongly inhibited by Ca2+ ions. Similarly, the ATPase activity was dependent on Mg2+ and inhibited by the presence of Ca2+ ions. The ATPase activity of the enzyme was largely insensitive to monovalent anions and cations, except for F-, which inhibited the vanadate-sensitive ATPase. Incubation of the enzyme in the presence of [14C]N-ethylmaleimide labeled the 115-kDa polypeptide, and this labeling could be prevented by the addition of ATP during the incubation. A reciprocal experiment showed that preincubation with N-ethylmaleimide inhibited the labeling of the 115-kDa polypeptide by [alpha-32P]ATP by UV illumination. This suggests a close proximity between the ATP-binding site and an essential sulfhydryl group. A possible connection between the isolated ATPase and organelle movement is discussed.
mesh_terms: D000251:Adenosine Triphosphatases / Q000302:isolation & purification* / Q000378:metabolism; D000345:Affinity Labels / Q000378:metabolism; D000818:Animals; D002837:Chromaffin Granules / Q000201:enzymology*; D002838:Chromaffin System / Q000201:enzymology*; D004591:Electrophoresis, Polyacrylamide Gel; D005033:Ethylmaleimide / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000201:enzymology*; D008970:Molecular Weight; D010777:Photochemistry; D006180:Proton-Translocating ATPases / Q000378:metabolism; D013379:Substrate Specificity; D014101:Torpedo; D014638:Vanadates / Q000494:pharmacology*
chemical_list: D000345:Affinity Labels; D014638:Vanadates; D000251:Adenosine Triphosphatases; D006180:Proton-Translocating ATPases; D005033:Ethylmaleimide