Characterization and solubilization of the membrane-bound ATPase of Mycoplasma gallisepticum

Abstract

The membrane-bound ATPase of Mycoplasma gallisepticum selectively hydrolyzed purine nucleoside triphosphates and dATP. ADP, although not a substrate, inhibited ATP hydrolysis. The enzyme exhibited a pH optimum of 7.0 to 7.5 and an obligatory requirement for divalent cations. Dicyclohexylcarbodiimide at a concentration of 1 mM inhibited 95% of the ATPase activity at 37°C, with 50% inhibition occurring at 22 μM dicyclohexylcarbodiimide. Sodium or potassium (or both) failed to stimulate activity by greater than 37%. Azide (2.6 mM), diethylstilbestrol (100 μg/ml), p-chloromercuribenzoate (1 mM), and vanadate (50 μM) inhibited 50, 91, 89, and 60%, respectively. The ATPase activity could not be removed from the membrane without detergent solubilization. Although most detergents inactivated the enzyme, the dipolar ionic detergent N-dodecyl-N,N-dimethyl-3-ammoni-1-propanesulfonate (0.1%) solubilized approximately 70% of the enzyme with only a minor loss in activity. The extraction led to a twofold increase in specific activity and retention of inhibition by dicyclohexylcarbodiimide and ADP. Glycerol greatly increased the stability of the solubilized enzyme. The properties of the membrane-bound ATPase are not consistent with any known ATPase. We postulate that the ATPase functions as an electrogenic proton pump.