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ELECTRON TRANSFER REACTIONS OCCURRING UPON LASER FLASH PHOTOLYSIS OF PHOSPHOLIPID BILAYER SYSTEMS CONTAINING CHLOROPHYLL, BENZOQUINONE AND CYTOCHROME c‐I. NEGATIVELY‐CHARGED VESICLES *
Author(s) -
Fang Yifei,
Tollin Gordon
Publication year - 1988
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.1751-1097.1988.tb02774.x
Subject(s) - chemistry , photochemistry , flash photolysis , cytochrome , cytochrome c , electron transfer , vesicle , benzoquinone , reaction rate constant , organic chemistry , membrane , kinetics , biochemistry , physics , quantum mechanics , mitochondrion , enzyme
— In negatively‐charged lipid bilayer vesicles prepared in deionized water from egg phosphatidylcholine and 25 mol % of α‐eleostearic acid, and containing chlorophyll a , benzoquinone, and cytochrome c , primary electron transfer after a laser flash occurred principally from chlorophyll triplet to benzoquinone, and to a smaller extent from chlorophyll triplet to oxidized cytochrome c . Several secondary electron transfer reactions occurred subsequent to this. The most rapid of these was electron transfer from reduced cytochrome c , which was bound to the outer surface of the negatively‐charged vesicle, to chlorophyll cation radical ( k = 3.9 times 10 3 s ‐1 ). Subsequent to this, the cation radical was reduced by benzoquinone anion radical ( k = 1.6 times 10 2 s ‐1 >) and bound oxidized cytochrome c was reduced by the remaining anion radical which was expelled into the aqueous phase by the negative charge on the vesicle surface. This latter reaction occurred at the membrane‐solution interface with an observed rate constant ( k = 60 s ‐1 ) two orders of magnitude smaller than cytochrome oxidation. Net reduced cytochrome c was produced in this process. The reduced cytochrome c was slowly reoxidized by benzoquinone ( k = 17 s ‐1 ) and the system was returned to its original state. When the vesicle system was made slightly basic by adding tris(hydroxymethyl)aminomethane, the rates of both the reverse electron transfer between chlorophyll cation radical and benzoquinone anion radical ( k = 5 times 10 2 s ‐1 ) and the oxidation of reduced cytochrome c by chlorophyll cation radical ( k = 9.4 times 10 3 s ‐1 ) were accelerated. The rate of reduction of oxidized cytochrome c by benzoquinone anion radical remained approximately the same.