The role of lipids and 17‐kDa protein in enhancing the recovery of O₂ evolution in cholate‐treated thylakoid membranes

Abstract

The recovery of 02 evolution of cholate-treated thylakoids induced by the simultaneous addition of the 17-and 23-kDa proteins was enhanced by the further addition of thylakoid total lipids up to about 75% of the non-depleted original broken thylakoids at the optimal concentration of the lipids, through reactivation of electron transfer between the sites of DPC donation and DCIP acceptance. Novel findings clarifing the cause of the discrepancies, with regard to the requirement for the 17-kDa protein on the 02 evolution of thylakoid membranes, were also provided, i.e., when the assay of 02 evolution for the reconstituted systems was carried out at a low level of NaCl (e.g., 0.1 mM), besides the 23-kDa protein, the 17-kDa protein was also required for 02 evolution, however, at a higher level of NaCl (>5 mM) the 17-kDa protein was not. The results suggest that the 17-kDa protein takes the place of Cl-or acts as a constituent protecting Cl-in the Cl-activating sites against fluctuation of the Cl-level in the inner compartment of thylakoid membranes. Photosystem II 02 evolution Reconstitution I7-kDa proteinClThylakoid Iipid

PsbP Protein, But Not PsbQ Protein, Is Essential for the Regulation and Stabilization of Photosystem II in Higher Plants

“…We also grew DPsbQ tobacco in a greenhouse (28°C, 700-1,000 mE m 22 s 21 in the daytime), and no significant difference was observed between DPsbQ and wild type (data not shown). In in vitro studies, PsbQ has been shown to be required for optimum PSII activity under low Cl 2 conditions (Akabori et al, 1984;Miyao and Murata, 1985) or under conditions in which the function of PsbP is impaired by truncation of its N terminus . However, such conditions are unlikely to occur naturally in vivo.…”

“…PsbO is responsible for the stable binding of the Mn cluster by facilitating Cl 2 retention in PSII (Miyao and Murata, 1984a). PsbP is involved in Ca 21 and Cl 2 retention in PSII (Ghanotakis et al, 1984a), and PsbQ mainly participates in Cl 2 retention (Akabori et al, 1984;Miyao and Murata, 1985). Finally, PsbP and PsbQ protect the Mn cluster from a bulky reductant (Ghanotakis et al, 1984b).…”

Absence of the PsbQ Protein Results in Destabilization of the PsbV Protein and Decreased Oxygen Evolution Activity in Cyanobacterial Photosystem II

“…The PsbO protein stabilizes the manganese cluster and is crucial for PS II oxygen evolution activity, whereas PsbP and PsbQ are necessary for oxygen evolution at physiological Ca 2ϩ and Cl Ϫ concentrations (2,(7)(8)(9)(10). Specifically, reconstitution of PsbP to PS II complexes containing PsbO reduces the Ca 2ϩ requirement, while further reconstitution of PsbQ restored oxygen evolution activity at a moderate rate at low concentrations of Cl Ϫ (9,11). These removal/reconstitution experiments indicate that PsbP and PsbQ offer the binding sites of Ca 2ϩ and Cl Ϫ ions or stabilize these ions within the PS II complex (2,(7)(8)(9).…”

A Truncated Mutant of the Extrinsic 23-kDa Protein that Absolutely Requires the Extrinsic 17-kDa Protein for Ca2+ Retention in Photosystem II

“…OEC17 has been reported to enhance Cl -retention in the PSII reaction center under low Cl -conditions (Ghanotakis et al 1984a, Akabori et al 1984, Miyao and Murata 1985. The functions of cyt c550 and the 12-kDa protein resemble to those of OEC23 and OEC17, but they are apparently different from OEC23 and OEC17 in both primary sequences and binding features to PSII complex (Seidler 1996, Enami et al 2000, and references cited therein).…”