Kinetic studies of chromaffin granule H+-ATPase and effects of bafilomycin A1.
Vacuolar type H+-ATPase purified from bovine chromaffin granules did not show simple Michaelis-Menten type kinetics, and had apparent Km values of 5 microM, 30 microM and 300 microM. These three Km values suggested the presence of catalytic cooperativity during steady-state hydrolysis. The single turnover rate was 10(-3)-fold the maximal velocity of the enzyme and similar to the rate estimated from the velocity of steady-state hydrolysis with the smallest Km value (5 microM). The H(+)-ATPase was inhibited by the stoichiometric binding of bafilomycin A1, a specific inhibitor of vacuolar type H(+)-ATPase. This inhibitor not only lowered the rate of ATP hydrolysis at the single catalytic site, but also affected the catalytic cooperativity of the enzyme.
Hanada
H
H
Department of Organic Chemistry and Biochemistry, Osaka University, Japan.
Moriyama
Y
Y
Maeda
M
M
Futai
M
M
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002417:Cattle; D002837:Chromaffin Granules / Q000187:drug effects / Q000201:enzymology*; D002838:Chromaffin System / Q000201:enzymology*; D006868:Hydrolysis; D007700:Kinetics; D018942:Macrolides; D013379:Substrate Specificity
D000900:Anti-Bacterial Agents; D018942:Macrolides; C040929:bafilomycin A1; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases