Reaction center of photosystem II with no peripheral pigments in D2 allows secondary electron transfer in D1.

A pigment-deficient reaction center of photosystem II (PSII)-with all the core pigments (two molecules of chlorophyll a and one of pheophytin a in each D protein) but with only one molecule each of peripheral chlorophyll a (Chlz) and beta-carotene (Car)-has been investigated by pump-probe spectroscopy. The data imply that Car and Chlz are both bound to D1. The absence of Car and Chlz in D2 allows the unprecedented observation of secondary electron transfer in D1 of PSII reaction centers at room temperature. The absorption band of the Car cation in D1 (Car(D1)(+*)) peaks around 910 nm (as against 990 nm for Car(D2)(+*)), and its positive hole is shared by ChlzD1, whereas Car(D2)(+*) can disappear by capturing an electron from ChlzD2.