title: Rapid degradation of the tetrameric Mn cluster in illuminated, PsbO-depleted photosystem II preparations.
abstract: A "decoupling effect" (light-induced electron transport without O2 evolution) was observed in Ca-depleted photosystem II (PSII(-Ca)) membranes, which lack PsbP and PsbQ (Semin et al. (2008) Photosynth. Res., 98, 235-249). Here PsbO-depleted PSII (PSII(-PsbO)) membranes (which also lack PsbP and PsbQ) were used to examine effects of PsbO on the decoupling. PSII(-PsbO) membranes do not reduce the acceptor 2,6-dichlorophenolindophenol (DCIP), in contrast to PSII(-Ca) membranes. To understand why DCIP reduction is lost, we studied light effects on the Mn content of PSII(-PsbO) samples and found that when they are first illuminated, Mn cations are rapidly released from the Mn cluster. Addition of an electron acceptor to PSII(-PsbO) samples accelerates the process. No effect of light was found on the Mn cluster in PSII(-Ca) membranes. Our results demonstrate that: (a) the oxidant, which directly oxidizes an as yet undefined substrate in PSII(-Ca) membranes, is the Mn cluster (not the Y(Z) radical or P680(+)); (b) light causes rapid release of Mn cations from the Mn cluster in PSII(-PsbO) membranes, and the mechanism is discussed; and (c) rapid degradation of the Mn cluster under illumination is significant for understanding the lack of functional activity in some PSII(-PsbO) samples reported by others.
authors.affiliation: Biological Faculty, Lomonosov Moscow State University, Moscow, Russia. semin@biophys.msu.ru
authors.forename: B K
authors.initials: BK
authors.lastname: Semin
authors.forename: L N
authors.initials: LN
authors.lastname: Davletshina
authors.forename: I I
authors.initials: II
authors.lastname: Ivanov
authors.forename: M
authors.initials: M
authors.lastname: Seibert
authors.forename: A B
authors.initials: AB
authors.lastname: Rubin
mesh_terms: D008027:Light; D008345:Manganese / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D018724:Spinacia oleracea / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D010940:Plant Proteins; C052389:oxygen-evolving enhancer protein 1, plant; D008345:Manganese; D010100:Oxygen