F1-like properties of an ATPase from the archaebacterium Halobacterium saccharovorum

For F1-ATPases from mitochondria and chloroplasts, tight binding of Mg2+ and ADP without Pi at a catalytic site had been reported as a cause of enzyme inhibition. The time dependence of this inhibition and the effect of various agents on this process have been described (Du, Z., and Boyer, P. D. (1990) Biochemistry 29, 402-407, and references therein). Similar results are now reported for the ATPase from Halobacterium saccharovorum. The nonlinear hydrolysis kinetics were modulated by nitrate, azide, sulfite, GTP, ADP in the absence of ATP, or Pi in characteristic ways, in good analogy with the effects of these agents on F1 enzymes. The similarity to the F1 systems suggests that it is tight ADP binding that is affected. Although these reactions of the H. saccharovorum ATPase occurred on different time and concentration scales than those of F1-ATPases, the two systems do not appear to be fundamentally different. The hydrolytic mechanism of the H. saccharovorum ATPase thus identifies this enzyme as a member of the F0F1-ATPase family.