A direct interaction between Photosystem I and the chloroplast coupling factor.

A regulation of the ATP-synthesizing complex by electron-transport rate has been found. The site of regulation could be localized within the Photosystem I region. The regulatory effect probably is produced by direct interactions between neighbouring charged protein complexes. The primary result is an increase in the percentage of those binding sites adopting a low-affinity state. This seems to lead to an enhanced leakage of protons out of the thylakoids, especially under those experimental conditions employing low nucleotide concentrations. Changes in the P/2e ratio can be observed, especially if the total ADP + ATP concentration used in the experiment is below 200 microM.