title: Bicarbonate requirement for the water-oxidizing complex of photosystem II.
abstract: It is well established that bicarbonate stimulates electron transfer between the primary and secondary electron acceptors, Q(A) and Q(B), in formate-inhibited photosystem II; the non-heme Fe between Q(A) and Q(B) plays an essential role in the bicarbonate binding. Strong evidence of a bicarbonate requirement for the water-oxidizing complex (WOC), both O2 evolving and assembling from apo-WOC and Mn2+, of photosystem II (PSII) preparations has been presented in a number of publications during the last 5 years. The following explanations for the involvement of bicarbonate in the events on the donor side of PSII are considered: (1) bicarbonate serves as an electron donor (alternative to water or as a way of involvement of water molecules in the oxidative reactions) to the Mn-containing O2 center; (2) bicarbonate facilitates reassembly of the WOC from apo-WOC and Mn2+ due to formation of the complexes MnHCO3+ and Mn(HCO3)2 leading to an easier oxidation of Mn2+ with PSII; (3) bicarbonate is an integral component of the WOC essential for its function and stability; it may be considered a direct ligand to the Mn cluster; (4) the WOC is stabilized by bicarbonate through its binding to other components of PSII.
authors: Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, 142290, Moscow Region, Russia. klimov@issp.serpukhov.su
authors: V V
authors: VV
authors: Klimov
authors: S V
authors: SV
authors: Baranov
mesh_terms: D001639:Bicarbonates / Q000737:chemistry* / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005561:Formates / Q000494:pharmacology; D008345:Manganese / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D014867:Water / Q000737:chemistry*
chemical_list: D001639:Bicarbonates; D005561:Formates; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014867:Water; C030544:formic acid; D008345:Manganese; D010100:Oxygen