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 μM, 30 μM and 300 μM. 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 μM). 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. © 1990.