Absorption changes in Photosystem II in the Soret band region upon the formation of the chlorophyll cation radical [P$_{D1}$P$_{D2}$]$^+$ - I2BC Access content directly
Journal Articles Photosynthesis Research Year : 2023

Absorption changes in Photosystem II in the Soret band region upon the formation of the chlorophyll cation radical [P$_{D1}$P$_{D2}$]$^+$

Miwa Sugiura
  • Function : Author
  • PersonId : 1287290
Makoto Nakamura
Ryo Nagao
Takumi Noguchi
A. William Rutherford
Julien Sellés
  • Function : Author
  • PersonId : 1225153

Abstract

Flash-induced absorption changes in the Soret region arising from the [P$_{D1}$P$_{D2}$]$^+$ state, the chlorophyll cation radical formed upon light excitation of Photosystem II (PSII), were measured in Mn-depleted PSII cores at pH 8.6. Under these conditions, Tyr$_D$ is $i$) reduced before the first flash, and $ii$) oxidized before subsequent flashes. In wild-type PSII, when Tyr$_D$$^•$ is present, an additional signal in the [P$_{D1}$P$_{D2}$]$^+$ -minus-[P$_{D1}$P$_{D2}$] difference spectrum was observed when compared to the first flash when Tyr$_D$ is not oxidized. The additional feature was "W-shaped" with troughs at 434 nm and 446 nm. This feature was absent when Tyr$_D$ was reduced, but was present ($i$) when Tyr$_D$ was physically absent (and replaced by phenylalanine) or ($ii$) when its H-bonding histidine (D2-His189) was physically absent (replaced by a Leucine). Thus, the simple difference spectrum without the double trough feature at 434 nm and 446 nm, seemed to require the native structural environment around the reduced Tyr$_D$ and its H bonding partners to be present. We found no evidence of involvement of P$_{D1}$ , Chl$_{D1}$ , Phe$_{D1}$ , Phe$_{D2}$ , Tyr$_Z$ , and the Cyt$b_{559}$ heme in the W-shaped difference spectrum. However, the use of a mutant of the P$_{D2}$ axial His ligand, the D2-His197Ala, shows that the P$_{D2}$ environment seems involved in the formation of "W-shaped" signal.
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hal-04217710 , version 1 (26-09-2023)

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Alain Boussac, Miwa Sugiura, Makoto Nakamura, Ryo Nagao, Takumi Noguchi, et al.. Absorption changes in Photosystem II in the Soret band region upon the formation of the chlorophyll cation radical [P$_{D1}$P$_{D2}$]$^+$. Photosynthesis Research, 2023, ⟨10.1007/s11120-023-01049-3⟩. ⟨hal-04217710⟩
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