Abstract
The characteristics of ATP synthesis in cell envelope vesicles of Halobacterium halobiurn were further studied. The results confirmed the previous conclusion (Mukohata et al. (1986) J. Biochem. 99, 1-8) that the ATP synthase in this extremely halophilic archaebacterium can not be an ordinary type of F0F1-ATPase, which has been thought to be ubiquitous among all the aerobic organisms on our biosphere. The ATP synthesis was activated most in 1M NaCl and/or KCl, and at 40°C, and at 80mM MgCl2 where F0F1-ATPase loses its activity completely. The synthesis was negligible at 10°C, and at 5mM MgCl2. The Km for ADP was about 0.3mM in the presence of 20mM P1, 1M NaCl, 80mM MgCl2 and 10mM PIPES at pH 6.8 and 20°C. The ATP synthesis was not inhibited by NaN3 and quercetin (specific inhibitors for F0F1-ATPase) or vanadate (for E1E2-ATPase) or ouabain (for Na+, K+-ATPase) or P1, P5-di (adenosine-5') pentaphosphate (AP5A, for adenylate kinase). The ATP synthesis was not inhibited by modification (pretreatment) with NaN3 or 5'-p-fluorosulfonylbenzoyladenosine (FSBA). On the contrary, the ATP synthesis was rather non-specifically inhibited by N-ethylmaleimide (NEM), trinitrobenzenesulfonate (TNBS), phenylglyoxal, and pyridoxal phosphate. 7-Chloro-4-nitrobenz-2-oxa-1, 3-diazole (NBD-Cl) as well as N, N'-dicyclohexylcarbodiimide (DCCD) was found to be a specific inhibitor at least partly, because the NBD-Cl inhibition was partly prevented by ADP added to the modification mixture.
