Flash-induced absorption changes in photosystem I at low temperature: evidence that the electron acceptor A 1 is vitamin K 1

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 sol1 2 ~ 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).