Relationship Between Photophosphorylation in Steady State and ⊿pH and ⊿Ψ
LI You-Ze, DU Zi-Yun(Shanghai Institute of Plant Physiology, Academia Sinica, Shanghai 200032)
The relationship between the electrochemical potential across the thylakoid membrane (△μH~+) and ATP formation in steady state is complicated. We observed that the role of △ψ in △μH~+, besides △pH, was appreciable for driving ATP formation in steady state: (1) The proton was consumed during simultaneous PSP reaction, thus causing a decrease in △pH (Fig. 1). (2) The inhibition of △pH and PSP by NH_4Cl and nigericin was syncronous (Fig. 2). (3) The permeability of membrane to proton was affected by CCCP, and thereby the H_(in)~+ efflux was accelerated, the concentration of H_(in)~+ and the amplitude of △pH were decreased, and the PSP reaction was inhibited (Fig. 3). The results in Fig. 3 indicated that PSP was more dependent on the concentration of H_(in)~+ than △pH in the hylakoid. (4) Under the action of gramicid in D (～5×10~(-8) mol/L) and valinomycin (～5×10~(-7) mol/L, +K~+), △ψ was almost eliminated, and no significant effect on △pH was found. But PSP was inhibited by ～30% (Gram) and ～50% (Val) respectively. This shows that 30%～50% energy source may be provided by △ψ in steady state PSP reaction (Fig. 4, 5, 6, Table 1). The relative contribution of △pH and △ψ in △μH~+ to the driving force of ATP formation is dependent on the development of H~+ and other ion movement. It also depends. on the permeability of various particles to ions and the ionic conditions in reactive medium.
【Fund】： 西德大众汽车厂基金;; 我国自然科学基金