File:Fpls-02-00028-g010.png

English: PSII crystal structure from thermophilic cyanobacterium Thermosynechococcus vulcanus (Courtesy of Jian-Ren Shen, personal communication, 2011 to the authors; see Umena et al., 2011). This figure shows the location of HC (bicarbonate) that is bound to non-heme iron (Fe2+; see blue circle in the center). Amino acids within 3.3 Å of HC are two tyrosines and one histidine: D1-Y246; D2-Y244; D1-H272. D2-K264 is not shown. (The concept has evolved in Govindjee's laboratory, beginning with the work of Alan Stemler, followed by extensive work of Thomas J. Wydrzynski, Paul Jursinic, Rita Khanna, Danny Blubaugh, Julian Eaton-Rye, Sarojini Bose, Fatima El-Shintinawy, Jack J.S. Van Rensen, Wim F.J. Vermaas, Chunhe Xu, Jinchiang Cao, and Jin Xiong (the latter two worked on cyanobacteria) that HC plays a key role on the electron-acceptor side of PSII.) These researchers among many others, have suggested that there is a unique role of HC in the electron flow from reduced QA to QB−, and proton transport to QB− (Van Rensen et al., 1999). The model shown here provides detailed information that will allow future experimenters to find the molecular mechanism of the HC effect on the PSII.