[Electron-transport chain of photosynthesis: Inactivation mechanism and stabilization].

The mechanism of inactivation of the electron-transport chain of chloroplasts within the framework of a previously described kinetic model based on two steps, i.e. activation of the electron-transport chain and its irreversible inactivation, was studied. It was found that activation results from a decrease in the transmembrane gradient of pH on the photosynthetic membrane during inactivation. The kinetics of irreversible inactivation of different parts of the electron-transport chain of chloroplasts were studied. The water decompositon system was shown to be the most labile part of the chain (at a point lying before the carrier accepting the electrons from 1,5-diphenylcarbazide). The inactivation kinetics of the electron-transport chain of chloroplasts under different environmental conditions were studied. The stabilizing effects of definite concentrations of hydrogens ions, glycerol and bovine serum albumin were demonstrated. The mechanisms of these effects are discussed. A 200-fold stabilization of the chloroplasts with respect to their irreversible inactivation due to optimization of the medium was achieved.