SPINACH FERREDOXIN REDUCTION BY MEMBRANE-BOUND CHLOROPHYLL TRIPLET STATE VIA A DIQUAT MEDIATOR

Abstract Laser flash photolysis experiments have shown that the diquat analog containing a propylene bridge (PDQ²⁺), when electrostatically bound to negatively-charged vesicles containing chlorophyll, is able to mediate the rapid reduction ( k = 1.1 × 10⁵ s^-1) of spinach ferredoxin via electron transfer quenching of triplet state chlorophyll. The kinetics of formation and decay of reduced ferredoxin are consistent with a mechanism involving complex formation between oxidized ferredoxin and vesicle-bound PDQ²⁺. Under optimal conditions, approximately 15% of the quenched triplets yield reduced ferredoxin. This process is a model for soluble ferredoxin reduction which occurs in green plant photosystem I, and results in an appreciable storage of electromagnetic energy in the reaction products.