Covalent binding of 1,N6-ethenoadenosine diphosphate to catalytic and noncatalytic sites of chloroplast ATP-synthase

The catalytic and noncatalytic sites of the chloroplast coupling factor (CF1) were selectively modified by incubation with the dialdehyde derivative of the fluorescent adenosine diphosphate analogue 1,N-6-ethenoadenosine diphosphate. The modified CF1 was reconstituted with EDTA-treated chloroplast thylakoid membranes. The influence of light-induced transmembrane proton gradient and of phosphate ions on the fluorescence of 1,N-6-ethenoadenosine diphosphate covalently bound to catalytic sites of reconstituted CF1(ATP-synthase) was studied. Upon illumination of thylakoid membranes with saturating white light, the quenching of fluorescence of covalently bound 1,N-6-ethenoadenosine diphosphate was observed. The quenching was reversed by the addition of inorganic phosphate to the reaction mixture in the dark. Repeated illumination induced the quenching once again: however, the addition of phosphate ions did not affect the fluorescence intensity now. When 1,N-6-ethenoadenosine diphosphate was covalently bound to noncatalytic sites of ATP-synthase, no similar fluorescent changes were observed. The interrelation of the observed changes of 1,N-6-ethenoadenosine diphosphate fluorescence and the mechanism of energy-dependent changes in the structure of the catalytic site of ATP-synthase is discussed.