Optimal conditions for cyclic photophosphorylation and electric potential generation have been established in well coupled Photosystem (PS)I-enriched subchloroplast vesicles supplemented with ferredoxin. Using NADPH and oxygen as redox-poising agents, it is shown that accurate redox poising of the cyclic system is required for optimal electron transfer. The molar ratio of NADPH to oxygen, rather than their concentrations, regulates the rate of cyclic photophosphorylation. In the present experimental system, the actual redox potential of ferredoxin is of crucial importance for optimal cyclic electron transfer and energy transduction. Under conditions for optimal redox poising of the cyclic system, a relatively strong expression of the flash-induced slow electric potential component was found, as monitored by the absorption changes of carotenoids and of oxonol VI. The function and regulation of cyclic electron transfer in stroma lamellae membranes in vivo are discussed in view of the lateral heterogeneity of redox components in chloroplast membranes.
- (Spinach chloroplast vesicle)
- Electric potential
- Electron transfer
- Photosystem I
- Redox potential