ELECTRON TRANSFER REACTIONS OCCURRING UPON LASER FLASH PHOTOLYSIS OF PHOSPHOLIPID BILAYER SYSTEMS CONTAINING CHLOROPHYLL, BENZOQUINONE AND CYTOCHROME c‐I. NEGATIVELY‐CHARGED VESICLES*

Abstract—In negatively‐charged lipid bilayer vesicles prepared in deionized water from egg phosphatidylcholine and 25 mol % of α‐eleostearic acid, and containing chlorophylla, benzoquinone, and cytochromec, primary electron transfer after a laser flash occurred principally from chlorophyll triplet to benzoquinone, and to a smaller extent from chlorophyll triplet to oxidized cytochromec. Several secondary electron transfer reactions occurred subsequent to this. The most rapid of these was electron transfer from reduced cytochromec, which was bound to the outer surface of the negatively‐charged vesicle, to chlorophyll cation radical (k= 3.9 times 103s‐1). Subsequent to this, the cation radical was reduced by benzoquinone anion radical (k= 1.6 times 102s‐1>) and bound oxidized cytochromecwas 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 cytochromecwas produced in this process. The reduced cytochromecwas 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 102s‐1) and the oxidation of reduced cytochrome c by chlorophyll cation radical (k= 9.4 times 103s‐1) were accelerated. The rate of reduction of oxidized cytochromecby benzoquinone anion radical remained approximately the same.