title: [Functions of pheophytin, plastoquinone, iron and carotenoids in plant photosystem 2 reaction centers].
abstract: Photoreduction of the intermediary electron acceptor, pheophytin (Ph), in photosystem-2 (PS-2) reaction centers of spinach chloroplasts or subchloroplast particles (TSF-II and TSF-IIa) at 220 K and Eh approximately -450 mV produces a narrow ESR signal of Ph. (g = 2.0033; delta H approximately 13 G) and a "doublet" centered at g = 2.00 with a splitting of 52 G at 7 K. The doublet (but not the narrow signal) is eliminated after extraction of lyophylized TSF-II with hexane, containing 0.1-0.2% methanol, or after extraction of Fe with LiClO4 and o-phenantroline, and the signal is restored by reconstitution with plastoquinone-A (PQ) or Fe++, respectively. The Fe removal results also in the development of a photoinduced ESR signal of PQ. (g approximately 2.0044; delta H approximately 9.2 G). The conclusion is made that the primary electron acceptor, Q, is in fact a complex PQ-Fe++ and that the exchange interaction of Ph. with PQ. -Fe++ is responsible for the ESR doublet. Photoreduction of Ph in TSF-IIa is accompanied by the 3-fold decrease in the formation of carotenoid triplet state (measured by the characteristic flash-induced absorbance changes) which is suggested to be a result of charge recombination in the pair [P680+ .PH.].
mesh_terms: D001665:Binding Sites; D002338:Carotenoids / Q000502:physiology*; D002734:Chlorophyll / Q000031:analogs & derivatives*; D002736:Chloroplasts / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D007501:Iron / Q000502:physiology*; D010084:Oxidation-Reduction; D010674:Pheophytins / Q000502:physiology*; D010788:Photosynthesis; D010971:Plastoquinone / Q000502:physiology*; D011809:Quinones / Q000502:physiology*
chemical_list: D010674:Pheophytins; D011809:Quinones; D002734:Chlorophyll; D002338:Carotenoids; D007501:Iron; D010971:Plastoquinone
vernacular_title: Issledovanie funktsii feofitina, plastokhinona, zheleza i karotinoidov v reaktsionnykh tsentrakh fotosistemy 2 rasteniĭ.