ON THE ROLE OF PLASTOCYANIN IN PHOTOSYNTHESIS AND A NEW INHIBITOR OF FERREDOXIN DEPENDENT REACTIONS.

By digitonin treatment of chloroplasts, followed by differential ultracentrifugation, stable particles are obtained which reduce NADP in illumination only if plastocyanin is added. The system requires ferredoxin, ferredoxin-NADP-reductase, an electron donor system and is saturated by 0.002 micromoles plastocyanin. KCN and salicylaldoxime inhibit the system. An effective inhibitor of ferredoxin dependent reactions was found in disalicylidene-propanediamine DSPD as shown by its behavior in photosynthetic reactions of isolated chloroplasts. DSPD inhibits photosynthesis and light-dependent glucose uptake, but not the Hill reaction with quinone, by intact Chlorella cells. This strongly supports the view that ferredoxin is the natural cofactor of cyclic photophosphorylation in vivo. Unexpectedly, however, DSPD does not inhibit photosynthetic nitrite reduction in Chlorella, which is also assumed to require ferredoxin. Author