The red-absorbing chlorophyll a antenna states of photosystem I: A hole-burning study of Synechocystis sp PCC 6803 and its mutants

Low temperature (4.2 K) absorption and hole-burned spectra are presented fo r the trimeric (wild-type, WT) photosystem I complex of the cyanobacterium Synechocystis sp. PCC 6803, its monomeric form, and mutants deficient in th e PsaF, K, L, and M protein subunits. High-pressure- and Stark-hole-burning data for the WT trimer are presented as well as its temperature-dependent Q(nu)-absorption and -fluorescence spectra. Taken as a whole, the data lead to assignment: of a new and lowest energy antenna Q(y)-state, located at 7 14 nm at low temperatures. It is this state that is responsible for the flu orescence in the low-temperature limit and not the previously identified an tenna Q(y)-state near 708 nm. The data indicate that the 714 nm state is as sociated with strongly coupled chlorophyll a molecules (perhaps a dimer) an d possesses significant charge transfer character. The red chlorophylls abs orbing at 708 and 714 nm do not appear to be directly bound to any of the a bove protein subunits. The results are consistent with a location close to the interfacial regions between PsaL and M and the PsaA/B heterodimeric cor e. It is likely that the red chlorophylls are bound to PsaA and/or PsaB.