title: Hypothesis: the peroxydicarbonic acid cycle in photosynthetic oxygen evolution.
abstract: Peroxydicarbonic acid (Podca), a proposed intermediate in photosynthetic oxygen evolution, was synthesized electrochemically. Consistent with literature descriptions of this compound, it was shown to be a highly reactive molecule, spontaneously hydrolyzed to H2O2, as well as susceptible to oxidative and reductive decomposition. In the presence of Mn2+ or Co2+, Podca was quickly broken down with release of O2. The liberation of O2, however, was partially suppressed at high O2 concentrations. In the presence of Ca-washed photosystem II-enriched membranes lacking extrinsic proteins, Podca was decomposed with the release of O2, but only under conditions favoring photosynthetic electron flow (light plus a Hill oxidant). A model is proposed that details how peroxydicarbonic acid could act as an oxygen-evolving intermediate. The hypothesis is consistent with the well-established Kok model and with recent findings related to the chemistry of oxygen evolution.
authors.affiliation: Section of Plant Biology, University of California, Davis, CA 95616, USA.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Castelfranco
authors.forename: Yih-Kuang
authors.initials: YK
authors.lastname: Lu
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Stemler
mesh_terms: D001639:Bicarbonates / Q000737:chemistry / Q000378:metabolism; D002256:Carbonic Anhydrases / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism*; D010463:Peracetic Acid / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D045332:Photosystem II Protein Complex; D008345:Manganese; D006861:Hydrogen Peroxide; D002256:Carbonic Anhydrases; D010463:Peracetic Acid; D010100:Oxygen