Effect of pH, salt, and coupling state on the interaction of ferredoxin with the chloroplast membrane

To determine if the interaction between ferredoxin and ferredoxin:NADP reductase is similar to the interaction between the purified proteins when the ferrodoxin:NADP reductase is membrane bound, the effect of pH, salt, and coupling state on the Km for ferredoxin in NADP reduction by chloroplast membranes has been examined. Increasing pH and salt concentrations as well as uncouplers all resulted in increases in the Km for ferredoxin. The pH and salt effects on the Km are similar to effects observed by others (C. Batie and H. Kamin (1981) J. Biol. Chem. 256, 7756-7763) on the dissociation constant for a complex between the two purified proteins, although the salt effect on the Km appears to be affected by the surface potential of the chloroplast membrane. These results suggest that the interaction between ferredoxin and the membrane-bound ferredoxin:NADP reductase is not greatly different from the interaction which has been characterized between the two purified proteins.