Functional characterization of an extremely thermophilic ATPase in membranes of the crenarchaeon Acidianus ambivalens

A plasma membrane-bound adenosine triphosphatase with specific activities u p to 0.2 mu mol min(-1) (mg protein)(-1) at 80 degrees C was detected in th e thermoacidophilic crenarchaeon Acidianus ambivalens (DSM 3772). The enzym atic activity exhibited a broad pH-optimum in the neutral range with two su boptima at pH 5.5 and 7.0, respectively. Sulfite activation resulted in onl y one pH optimum at 6.25. In the presence of the divalent cations Mg2+ and Mn2+ the ATPase activity was maximal. Remarkably, the hydrolytic rates of G TP and ITP were substantially higher than for ATP. ADP and pyrophosphate we re only hydrolyzed with small rates, whereas AMP was not hydrolyzed at all. both activities could be weakly inhibited by the classical F-type ATPase i nhibitor N,N'-dicyclohexylcarbodiimide, whereas azide had no influence at a ll. The classical inhibitor of V-type ATPases, nitrate, also exerted a smal l inhibitory effect. The strongly specific V-type ATPase inhibitor concanam ycin A, however, showed no effect at all. The P-type ATPase inhibitor vanad ate had no inhibitory effect on the ATPase activity at pH 7.0, whereas a re markable inhibition at high concentrations could be observed for the activi ty at pH 5.5. Arrhenius plots for both membrane bound ATPase activities wer e linear up to 95 degrees C, reflecting the enormous thermostability of the enzyme.