On the ion transport system of photosynthesis — Investigations on a molecular level —

Abstract

1. The Chl-b reaction in chloroplasts is biphasic. 2. Both the slow phase (~ 10-1 sec) and the fast phase (≪ 10-1 sec) are caused by ion exchange across the thylakoid membrane. 3. The slow phase is caused by an intrinsic slow ion exchange (H®) across an undamaged membrane (The permeability for arbitrary ions is lower than for H®). 4. The fast phase is caused by an enhanced ion exchange across a damaged membrane. Damaging can be systematically caused, for instance, by membrane holes made by osmotic procedures, or by specific pores for alkaline ions made by gramicidin. 5. The function unit of the intrinsic slow ion exchange (H®) has been identified as being the membrane of one whole undamaged thylakoid. 6. The electron transport in undamaged thylakoid membranes is coupled to the intrinsic ion transport (H®). 7. Phosphorylation is coupled to an additional intrinsic ion transport (H®). 8. Leaks of the order of only one pore cause a collapse from the intrinsic slow phase (10-1 sec) into the fast phase of ion exchange (< 10-1 sec). 9. The ratio of the amplitude of the slow and fast phases indicates the ratio of thylakoids which are undamaged and damaged. 10. The Chl-b reaction indicates an electrical field across the thylakoid membrane. This field promotes the ion exchanges discussed above. 11. The potential difference amounts to about 250 mV. 12. The field is built up in light within ≤ 2·10-8 sec 29, 30. 13. These results give a first direct insight into the properties of membranes on a molecular level. They serve as a valuable means for deciding between the different hypotheses on the mechanism of phosphorylation.