Relationship between P700 turnover (m second) and NADP reduction as a function of ferredoxin concentration in isolated broken chloroplasts

Steady-state electron flux through P₇₀₀ (t $\text{1}\text{2}$ 20 msec) and concomitant rate of NADP reduction have been measured under weak actinic illumination as a function of concentration of ferredoxin added to broken chloroplasts isolated from peas. At suboptimal concentrations of ferredoxin this P₇₀₀ is not sufficient to account for the NADP reduction. At high concentrations ferredoxin inhibits the rate of NADP reduction without affecting the P₇₀₀ flux under short wavelength illumination. Under far red illumination P₇₀₀ flux is also inhibited by ferredoxin at high concentrations. Addition of 5 mM Mg⁺⁺ increases the rate of NADP reduction at all concentrations of ferredoxin under both kinds of illumination, while P₇₀₀ flux is inhibited under short wavelength illumination and remains unchanged under far red illumination. The results indicate that the observed (20 msec) P₇₀₀ is not involved in NADP reduction.