Abstract— 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, QA‐. 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.
|Number of pages
|Photochemistry and Photobiology
|Published - May 1986