INTERACTION OF MG+2 WITH BEEF-HEART MITOCHONDRIAL ATPASE (F-1)

The soluble mitochondrial ATPase, F1, can be slowly inactivated by incubation with Mg+2 in a manner consistent with the observations of Moyle and Mitchell (FEBS Lett. 56, 55 (1975)). This inhibition results in a low initial rate of ATP hydrolysis upon addition to an ATPase assay medium of F1 which has been incubated with Mg+2. This inhibition, however, is completely reversible by Mg·ATP in a time dependent process and results in the rate of ATP hydrolysis increasing during the ATPase assay to reach control levels after 30 sec. The length of the lag is independent of the F1 concentration in the ATPase assay and the lag is also completely reversed by subsequent incubation with excess EDTA before assay. F1 is unstable if incubated with EDTA in the absence of free nucleotides or Mg+2. The rate of inactivation increases with decreasing protein concentration until a limiting rate is reached at high dilution. Mg+2 in excess of the EDTA or 50 μM ADP stabilize the F1 against the inactivation but cannot reverse prior denaturation. © 1979.