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BIMANES—26. AN ELECTRON TRANSFER REACTION BETWEEN PHOTOSYSTEM I1 AND MONOBROMOBIMANE INDUCES STATIC CHLOROPHYLL a QUENCHING IN SPINACH CHLOROPLASTS
Author(s) -
Melis Anastasios,
Kosower Nechama S.,
Crawford Nancy A.,
KirowaEisner Emilia,
Schwarz Miriam,
Kosower Edward M.
Publication year - 1986
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1986.tb09537.x
Subject(s) - chemistry , photochemistry , photosystem ii , light harvesting complexes of green plants , electron transfer , quantum yield , p680 , chlorophyll fluorescence , photosystem i , p700 , chloroplast , quenching (fluorescence) , fluorescence , chlorophyll , photosynthesis , biochemistry , organic chemistry , physics , quantum mechanics , gene
— Monobromobimane in chloroplasts lowers both the quantum yield of system II photochemistry and the yield of chlorophyll a fluorescence. Illumination of the chloroplasts in the presence of monohromobimane is an absolute prerequisite to the manifestation of this phenomenon, which proceeds via the Photosystem II intermediate, the semiquinone radical anion, Q A ‐. The latter transfers an electron to monobromobimane to yield an anion radical (mBBr · ), which may either lose bromide ion to yield a reactive radical (mB · ), or acquire a proton and undergo further reduction, eventually forming syn‐(methyl, methyl) bimane. In turn, mB reacts with the protein of the light‐harvesting complex, to form a product which acts as static excitation energy quencher in the chlorophyll pigment bed of photosystem 11. Polarographic reduction of monobromobimane shows an adsorption wave at O V and two reduction waves. Prolonged reduction in water at ‐0.5 V yields syn‐(methyl, methyl) bimane (which is further reduced at more negative potentials) and bromide ion. Thus, both electrochemical and chloroplast‐induced reduction produce syn‐(methyl, methyl) bimane. Monobromobimane may then serve as a Photosystem II activated probe in elucidating the conformation of intrinsic thylakoid membrane polypeptides.