Biochemistry (Washington) 1999-10-12

On the stator of rotary ATP synthase: the binding strength of subunit delta to (alpha beta)3 as determined by fluorescence correlation spectroscopy.

K Häsler, O Pänke, W Junge

Index: Biochemistry 38(41) , 13759-65, (1999)

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Abstract

ATP synthase is conceived as a rotary enzyme. Proton flow drives the rotor (namely, subunits c12 epsilon gamma) relative to the stator (namely, subunits ab2 delta(alpha beta)3) and extrudes spontaneously formed ATP from three symmetrically arranged binding sites on (alpha beta)3 into the solution. We asked whether the binding of subunit delta to (alpha beta)3 is of sufficient strength to hold against the elastic strain, which is generated during the operation of this enzyme. According to current estimates, the elastically stored energy is about 50 kJ/mol. Subunit delta was specifically labeled without impairing its function. Its association with solubilized (alpha beta)3 gamma in detergent-free buffer was studied by fluorescence correlation spectroscopy (FCS). A very strong tendency of delta to dimerize in detergent-free buffer was apparent (K(d)