Electron transfer from A−1to an iron‐sulfur center witht= 200 ns at room temperature in photosystem I Characterization by flash absorption spectroscopy

Forward electron transfer in intact photosystem I particles fromSynechococcussp. at room temperature has been studied by flash absorption spectroscopy with a time resolution of 5 ns. A kinetic phase witht = 200 ns was resolved and characterized by its absorption difference spectrum between 325 and 495 nm. This phase is attributed to electron transfer from the reduced redox center A1to an iron‐sulfur center, probably Fx. The difference spectrum for the reduction of A1is evaluated and the previously proposed identification of A1with vitamin K1is discussed.