Chapter 5 - NITROGEN FIXATION IN PHOTOSYNTHETIC BACTERIA

Abstract

Publisher Summary This chapter discusses ion gradients across chloroplast membranes as a form of energy storage while keeping in mind that ion fluxes may contribute to the regulation of photosynthetic activity. Major amounts of energy have been observed stored in the form of H+ gradients. The magnitude of the electric gradient (Δψ) associated with H+ uptake in chloroplasts rests primarily on the interpretation of experiments on the light-induced absorbance increase in the region of 515 nm. Thus, H+ uptake in chromatophores and chloroplasts probably generates a membrane potential at a steady state. The magnitude of this potential is probably less in chloroplasts than in chromatophores, possibly because chloroplasts are more permeable to ions such as Cl−. In the initial period of H+ uptake, the magnitude of the membrane potential should be higher. In flashing light, ATP formation can take place, but an H+ concentration gradient is not formed. Presumably, a membrane potential is formed as 518 nm absorption change is observed in flashing light. Thus, the dissipation of a membrane potential under conditions where an H+ concentration gradient cannot be formed may be sufficient to inhibit phosphorylation in chloroplasts.