Flash‐induced absorption changes in photosystem I at low temperature: evidence that the electron acceptor A₁is vitamin K₁

Abstract

Low temperature flash absorption spectroscopy has been applied to elucidate the chemical nature of the secondary electron acceptor A 1 of photosystem I (PS‐I). The flash‐induced absorption changes measured in digitonin‐fractionated spinach PS‐I particles at 10 K between 240 and 525 nm are shown to comprise a major decay phase with t ~ 150 μs which has been attributed to the recombination reaction P‐700 + ·A 1 → P‐700·A 1 [(1984) Biochim. Biophys. Acta 767, 404‐414]. We present the absorption difference spectrum of this reaction and demonstrate that it contains contributions in the ultraviolet due to A 1 , which are characteristic of vitamin K 1 (phylloquinone).