Light-dependent Modification of Spinach Chloroplast Coupling Factor 1 by Permanganate Ion

Treatment of spinach chloroplasts with 25 to 100 µm potassium permanganate in the presence of light, magnesium, and ADP gives rise to 35 to 60% inhibition of the subsequent phosphorylation and ATPase activities. For half-maximal inhibition, 5 to 10 µm ADP is necessary and ADP is not replaceable by other nucleotides. The light requirement can be met by preillumination as well as by an acid bath of the chloroplasts. The presence of any one of the substances, Pi, arsenate, ATP, or NH4Cl protects the enzyme against permanganate inhibition. Comparison of electron transport rates and pH rise of the control chloroplasts with those of permanganate-treated chloroplasts indicates that permanganate treatment makes the chloroplasts insensitive to ATP-induced stimulation of pH rise and to inhibition of electron transport by ATP. Kinetic analysis of trypsin-activated Ca2+-ATPase activity indicates that as a result of permanganate treatment the affinity of chloroplast coupling factor 1 for ATP has decreased and that the inhibition of this ATPase by ADP has switched from allosteric to competitive. Thus, permanganate seems to modify chloroplast coupling factor 1 and change its control functions by attacking at a site which is only rendered accessible in the presence of ADP and Mg2+ in an energized state of the chloroplasts.