A regulatory effect of the electron transport chain on the ATP synthase.

By the application of different experimental conditions, a variation of the apparent affinity of the chloroplast coupling factors 0-1 (CF0CF1) complex toward nucleotides was observed. This effect was paralleled by varying P/e2 ratios even in presence of millimolar ADP concentrations. This observations indicates that the electron transport system has a regulatory effect on the ATP synthase system. Different effects of mobile ionophores (uncouplers) and channel forming ionophores (gramicidin), respectively, indicated that either membrane-oriented charges--probably protons--or an electric potential difference was involved in the regulatory mechanism. When measuring photosystem II-dependent effects only, no regulation of the CF0CF1 complex could be detected in physiologically intact thylakoid preparations. This means that the regulatory active site must be localized between the 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, (DBMIB) inhibition site and the methylviologen acception site.