Light modulation of chloroplast membrane-bound ferredoxin-NADP+ oxidoreductase.

Light increases the affinity of chloroplast membrane-bound ferredoxin-NADP+ oxidoreductase for its physiological substrates in NADP+ photoreduction, that is, NADP+ and ferredoxin. Light may cause this effect through a conformational change of the enzyme related to the formation of a light-driven delta pH since the effect is prevented by uncouplers. Although the external pH does influence the extent of photoreduction of NADP+ in saturating light, it does not significantly influence the extent of the energy-driven change in affinity of the enzyme for its substrates.