title: Isolation of ATPase I, the proton pump of chromaffin-granule membranes.
abstract: Chromaffin-granule membranes contain two ATPases, which can be separated by (NH4)2SO4 fractionation after solubilization with detergents, or by phase segregation in Triton X-114. ATPase I (Mr 400000) is inhibited by trialkyltin, quercetin and alkylating agents, and hydrolyses both ATP and ITP. It contains up to five types of subunit, including a low-Mr hydrophobic polypeptide that reacts with dicyclohexylcarbodi-imide; these subunits are unrelated to those of mitochondrial F1F0-ATPase, as judged by size and reaction with antibodies. ATPase II (Mr 140000) is inhibited by vanadate, and is specific for ATP; it has not been extensively purified. Proton translocation by resealed chromaffin-granule 'ghosts', measured by uptake of methylamine or by quenching of the fluorescence of 9-amino-6-chloro-2-methoxyacridine, is supported by the hydrolysis of ATP or ITP, and inhibited by quercetin or alkylating agents, but not by vanadate. ATPase I must therefore be the proton translocator involved in the uptake of catecholamines and possibly of other components of the chromaffin-granule matrix, whereas ATPase II does not translocate protons.
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D002837:Chromaffin Granules / Q000201:enzymology*; D002838:Chromaffin System / Q000201:enzymology*; D003902:Detergents; D004591:Electrophoresis, Polyacrylamide Gel; D006868:Hydrolysis; D007293:Inosine Triphosphate / Q000378:metabolism; D007425:Intracellular Membranes / Q000201:enzymology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D010446:Peptide Fragments / Q000032:analysis; D011522:Protons; D011794:Quercetin / Q000494:pharmacology
chemical_list: D003902:Detergents; D007527:Isoenzymes; D010446:Peptide Fragments; D011522:Protons; D007293:Inosine Triphosphate; D011794:Quercetin; D000251:Adenosine Triphosphatases