Nucleotide Binding and ATPase Activity of Membrane Bound Chloroplast Coupling Factor (CFj)

Bernhard Huchzermeyer Botanisches Institut, Tierärztliche Hochschule, Bünteweg 17d, D-3000 Hannover 71, Bundesrepublik Deutschland Z. Naturforsch. 43c, 133-139 (1988); received June 19, 1987 Chloroplasts, CF0CF,, Light Triggered ATPase Activity, Regulation. Mechanism of Inactivation It has been found that the decay of light triggered ATPase activity is paralleled by nonexchangeable type of binding of one ADP per mol of CF,. Inactivation of light triggered ATPase activity is a continuous process. It can be described mathematically as shown in this paper. Three simplified reaction schemes are described, each of them describing the mode of ATPase inactivation in a mechanistic way. A computer simulation of each model was performed and the results were compared to the observed experimental data. In the presence of phosphate our results were explained best by a model assuming that there is at first a rapid binding of ADP to "exchangeable" sites. Due to a slowly occurring change in the CF, protein with prolonged incubation, an increasing portion of the nucleotides can be found bound in a non-exchangeable way after some seconds of incubation. Our model does not rule out that this reaction sequence might be a part of a catalytic cycle in vivo. — Another result was the finding that there is an additional diminution of ATPase activity when phosphate is lacking.