TABLE 2.

ATPase activities of MB and soluble F_1Cp or F₁F_oCp after extraction with EDTA and detergent^a

Treatment	Protein (mg)	Activityb		Activity (U · mg−1) in the presence of c:
		U	U · mg−1	DCCD (100 μM)	Na azide (1 mM)
None	9.40	0.800	0.085	0.045	0.024
Membrane + DM
Residual membrane	4.39	0.108	0.024	0.020	0.019
Extracts (F1Fo)	5.24	1.198	0.228	0.125	0.073
Membrane + EDTA
Residual membrane	7.32	0.240	0.033	0.022	0.020
Extracts (F1)	2.22	0.942	0.424	0.330	0.135

^aFor solubilization of F₁F_o, washed membranes (2 mg/ml) were suspended in TMG buffer containing Na ATP (1 mM), DM (1% [wt/vol]), and PMSF (0.1 mM); the suspension was incubated on ice for 1 h and centrifuged at 100,000 × g for 1 h. The supernatant containing soluble F₁F_o was collected, and the pellet containing residual membranes was washed and resuspended in TMG buffer. For solubilization of F₁, washed membranes (1 mg/ml) were subjected to similar treatments, except that the membranes were suspended in 100 mM Tris-HCl (pH 8.0)-15 mM EDTA-2 mM LiCl-1 mM ATP. EDTA was removed from the extracts by dialysis against TMG buffer containing 1 mM Na ATP. The pellet containing residual membranes was washed and resuspended in TMG buffer. ATPase assays were done with Na ATP (2 mM) as a substrate.

^bOne unit of activity is defined as 1 μmol of P₁ released per min.

^cDCCD or Na azide was added to assay mixtures, which were incubated at 37°C for 10 min prior to the start of ATPase assays by the addition of ATP.