Glycinebetaine, a compatible osmolyte of halotolerant plants and bacteria, partially protected photosystem (PS) 1 and PS2 electron transport reactions against thermal inactivation but with different efficiencies. In its presence, the temperature for half-maximal inactivation (t1/2) was generally shifted downward by 3-12 °C. Glycinebetaine stabilized photoinduced oxygen evolving reactions of PS2 by protecting the tetranuclear Mn cluster and the extrinsic proteins of this complex. A weaker, although noticeable, stabilizing effect was observed in photoinduced PS2 electron transport reactions that did not originate in the oxygen-evolving complex (OEC). This weaker protection by glycinebetaine was probably exerted on the PS2 reaction centre. Glycinebetaine protected also photoinduced electron transport across PS1 against thermal inactivation. The protective effect was exerted on plastocyanin, the mobile protein in the lumen that carries electrons from the integral cytochrome b6f complex to the PS1 complex. and Y. M. Allakhverdieva ... [et al.].
The steady-state oxygen evolution rate was previously shown to be stimulated by the disaccharide trehalose in PSII suspension. Here we showed a similar increase in the rate of oxygen evolution in PSII core complexes from spinach in solution and in proteoliposomes in the presence of trehalose. Using direct electrometrical technique, we also revealed that trehalose had no effect on the kinetics of electron transfer from Mn to redox-active-tyrosyl radical, YZ (S1 - S2 transition), while it accelerated the kinetics of electrogenic proton transport during S2 - S3 and S4 - S0 transitions of the wateroxidizing complex (WOC) induced by the first, second, and third laser flashes in dark-adapted PSII samples. These observations imply that the effect of trehalose occurrs due to its interaction with the WOC., M. D. Mamedov, E. S. Nosikova, L. A. Vitukhnovskaya, A. A. Zaspa, A. Yu. Semenov., and Obsahuje bibliografické odkazy