Bicarbonate is an essential constituent of the water-oxidizing complex of photosystem II

S. I. Allakhverdiev, I. Yruela, R. Picorel, V. V. Klimov

    Research output: Contribution to journalArticlepeer-review

    73 Citations (Scopus)


    It is shown that restoration of photoinduced electron flow and O2 evolution with Mn2+ in Mn-depleted photosystem II (PSII) membrane fragments isolated from spinach chloroplasts is considerably increased with bicarbonate in the region pH 5.0-8.0 in bicarbonate-depleted medium. In buffered solutions equilibrated with the atmosphere (nondepleted of bicarbonate), the bicarbonate effect is observed only at pH lower than the pK of H2CO3 dissociation (6.4), which indicates that HCO3/- is the essential species for the restoration effect. The addition of just 2 Mn2+ atoms per one PSII reaction center is enough for the maximal reactivation when bicarbonate is present in the medium. Analysis of bicarbonate concentration dependence of the restoration effect reveals two binding sites for bicarbonate with apparent dissociation constant (K(d)) of ≃2.5 μM and 20-34 μM when 2,6- dichloro-p-benzoquinone is used as electron acceptor, while in the presence of silicomolybdate only the latter one remains. Similar bicarbonate concentration dependence of O2 evolution was obtained in untreated Mn- containing PSII membrane fragments. It is suggested that the K(d) of 20-34 μM is associated with the donor side of PSII while the location of the lower K(d) binding site is not quite clear. The conclusion is made that bicarbonate is an essential constituent of the water-oxidizing complex of PSII, important for its assembly and maintenance in the functionally active state.

    Original languageEnglish
    Pages (from-to)5050-5054
    Number of pages5
    JournalProceedings of the National Academy of Sciences of the United States of America
    Issue number10
    Publication statusPublished - May 13 1997


    • donor side
    • manganese
    • oxygen evolution

    ASJC Scopus subject areas

    • General


    Dive into the research topics of 'Bicarbonate is an essential constituent of the water-oxidizing complex of photosystem II'. Together they form a unique fingerprint.

    Cite this