The role of cyclic photophosphorylation in vivo

When cyclic photophosphorylation is inhibited in Chlorella vulgaris cells by carbonylcyanide-trifluoromethoxy phenylhy-drazone, photosynthetic CO₂-fixation under anaerobic conditions exhibits a distinct lag. Under the same conditions, the light-dependent formation of ribulose diphosphate shows also this lag. It is concluded that cyclic photophosphorylation is required to fill up the pools of phosphorylated intermediates of the Calvin cycle at a time when noncyclic photophosphorylation cannot yet efficiently operate. Under aerobic conditions, the initial energy demand can be accommodated by respiratory ATP or cyclic photophosphorylation or both. Evidence for stoichiometric participation of cyclic photophosphorylation in photosynthesis is still lacking.