Summary: The membrane-bound ATPase of the halophilic and alkaliphilic phototrophic bacterium was solubilized by washing membranes with buffer of low ionic strength and purified by ion-exchange chromatography, ultrafiltration and gel filtration. The of the trypsin-activated enzyme as determined by gel chromatography was approximately 400000. Four subunits were found by SDS electrophoresis with apparent M values of 58000, 53700, 46800 and 36900. The purified enzyme was cold labile, but was more stable at room-temperature and in the presence of -aminobenzamidine. Both the membrane-bound and the solubilized enzyme were inhibited by DCCD after preincubation, but not by oligomycin. The ATPase was activated by bicarbonate and sulphite. NaCl was inhibitory at low concentrations. The results are discussed with respect to optimum growth conditions for and its cytoplasmic solute concentrations. Responses of the enzyme to salts are compared to those of ATPases from two other halophilic bacteria.


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