Rapid Degradation of the Tetrameric Mn Cluster in Illuminated, PsbO-Depleted Photosystem II Preparations

B. K. Semin, L. N. Davletshina, I. I. Ivanov, M. Seibert, A. B. Rubin

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12 Scopus Citations

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 YZ 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.

Original languageAmerican English
Pages (from-to)152-156
Number of pages5
JournalBiochemistry (Moscow)
Volume77
Issue number2
DOIs
StatePublished - Feb 2012

NREL Publication Number

  • NREL/JA-2700-53433

Keywords

  • manganese
  • oxygen-evolving complex
  • photosystem II
  • PsbO extrinsic protein

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