Identification of the photochemically iodinated amino-acid residue on Dl-protein in the Photosystem II core complex by peptide mapping analysis

Yuichiro Takahashi, Kimiyuki Satoh

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11 Citations (Scopus)


The Dl-protein is exclusively iodinated in the Photosystem II core complex (Takahashi, Y., Takahashi, M. and Satoh, K. (1986) FEBS Lett. 208, 347-351) as a result of photooxidation of iodide in the secondary electron donor (Z). The photochemically iodinated protein was subjected to a peptide mapping analysis after partial chemical and proteolytic cleavages in order to identify the iodo-labeled amino-acid residue(s). The cleavage at the C-terminal side of tryptophan by N-chlorosuccinimide, methionine by CNBr, and glutamic acid by Staphylococcus aureus V8 proteinase indicated that the iodination site is restricted, in each case, to specific peptide fragments of apparent molecular mass of 14.5, 3 and 8 kDa, which presumably correspond to Ile-143-Trp-278, Arg-140-Met-172 and Leu-133-GIu-189, respectively, in the deduced sequence of spinach Dl-protein. The conclusion reached from this analysis is that the overlapping sequence among these three fragments, which starts at He-143 and ends at Met-172, and which contains two tyrosine residues of potential iodination site at the position of 147 and 161, carries the specific photochemical iodination site(s). When the surface-exposed tyrosine and histidine residues on Dl-protein in the Photosystem II core complex were subjected to iodination in the dark using Iactoperoxidase/H2O2 system, the Arg-140-Met-172 fragment was not iodinated, indicating that the photochemical iodination site is present in the interior part of the complex, in accordance with the folding model of D1-protein in the Photosystem II reaction center. Since Tyr-161 on D1-protein is predicted to be close to the putative His ligands for P-680 on the lumenal side of thylakoid membrane, it was concluded that this Tyr, rather than Tyr-147, which is present on the stromal side,was the photochemical iodination site. Symmetry consideration of the sequence of D1- and D2-proteins, together with EPR spectral shape, led us toconclude further, in agreement with the proposal based on the recent site-directed mutagenesis for the signal Us species on D2-protein, that the Tyr-161 on Dl-protein alone constituted the secondary electron donor (Z) of the Photosystem II reaction center.

Original languageEnglish
Pages (from-to)138-146
Number of pages9
JournalBBA - Bioenergetics
Issue number2
Publication statusPublished - Feb 1989


  • Dl-protein
  • Electron donor(Z)
  • Peptide mapping
  • Photosystem II
  • Tyrosine residue

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology


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