Abstract
The photoproduction of superoxide anion radical (O2−•) and hydrogen peroxide (H2O2) in photosystem II (PSII) preparations depending on the damage to the water-oxidizing complex (WOC) was investigated. The light-induced formation of O2−• and H2O2 in the PSII preparations rose with the increased destruction of the WOC. The photoproduction of superoxide both in the PSII preparations holding intact WOC and the samples with damage to the WOC was approximately two times higher than H2O2. The rise of O2−• and H2O2 photoproduction in the PSII preparations in the course of the disassembly of the WOC correlated with the increase in the fraction of the low-potential (LP) Cyt b559. The restoration of electron flow in the Mn-depleted PSII preparations by exogenous electron donors (diphenylcarbazide, Mn2+) suppressed the light-induced formation of O2−• and H2O2. The decrease of O2−• and H2O2 photoproduction upon the restoration of electron transport in the Mn-depleted PSII preparations could be due to the re-conversion of the LP Cyt b559 into higher potential forms. It is supposed that the conversion of the high potential Cyt b559 into its LP form upon damage to the WOC leads to the increase of photoproduction of O2−• and H2O2 in PSII.
Highlights
Photosystem II (PSII) is a pigment–protein complex built into the thylakoid membrane
The complete removal of Mn ions from the water-oxidizing complex (WOC) by NH2 OH treatment led to a 5-fold decrease in the ∆F (Figure 1(I)A, curve 4) due to the loss of electron donation from the Mn-containing WOC to the PS II reaction centre (RC), which is in accordance with previous publications [28]
The obtained results demonstrate that the step-by-step disassembly of the WOC leading to the suppression of electron transport from the WOC to RC stimulates H2O2 and O2− photoproduction in photosystem II (PSII), and, among the samples, the Mn-depleted PSII preparations
Summary
Photosystem II (PSII) is a pigment–protein complex built into the thylakoid membrane. The sequential absorption of photons and charge separation in the RC result in the formation of intermediate states (S0 –S4 ) of the WOC, and the transition from S4 to S0 is accompanied by the oxygen release
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