title: The Mechanisms of Oxygen Reduction in the Terminal Reducing Segment of the Chloroplast Photosynthetic Electron Transport Chain.
abstract: The review is dedicated to ascertainment of the roles of the electron transfer cofactors of the pigment-protein complex of PSI, ferredoxin (Fd) and ferredoxin-NADP reductase in oxygen reduction in the photosynthetic electron transport chain (PETC) in the light. The data regarding oxygen reduction in other segments of the PETC are briefly analyzed, and it is concluded that their participation in the overall process in the PETC under unstressful conditions should be insignificant. Data concerning the contribution of Fd to the oxygen reduction in the PETC are examined. A set of collateral evidence as well as results of direct measurements of the involvement of Fd in this process in the presence of isolated thylakoids led to the inference that this contribution in vivo is negligible. The increase in oxygen reduction rate in the isolated thylakoids in the presence of either Fd or Fd plus NADP+under increasing light intensity was attributed to the increase in oxygen reduction executed by the membrane-bound oxygen reductants. Data are presented which imply that a main reductant of the O2molecule in the terminal reducing segment of the PETC is the electron transfer cofactor of PSI, phylloquinone. The physiological significance of characteristic properties of oxygen reductants in this segment of the PETC is discussed.
authors.affiliation: Photosynthetic Electron Transport lab., Institute of Basic Biological Problems, Pushchino, 142290, Russia.
authors.forename: Marina A
authors.initials: MA
authors.lastname: Kozuleva
authors.affiliation: Photosynthetic Electron Transport lab., Institute of Basic Biological Problems, Pushchino, 142290, Russia ivboni@rambler.ru.
authors.forename: Boris N
authors.initials: BN
authors.lastname: Ivanov
mesh_terms: D002736:Chloroplasts / Q000378:metabolism*; D004579:Electron Transport; D005288:Ferredoxins / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis
chemical_list: D005288:Ferredoxins; D010100:Oxygen
keywords: Chloroplast; Electron transport; Ferredoxin; Oxygen reduction; Photosystem I; Phylloquinone