An overview on chlorophylls and quinones in the photosystem I-type reaction centers.

Minor but key chlorophylls (Chls) and quinones in photosystem (PS) I-type reaction centers (RCs) are overviewed in regard to their molecular structures. In the PS I-type RCs, the prime-type chlorophylls, namely, bacteriochlorophyll (BChl) a' in green sulfur bacteria, BChl g' in heliobacteria, Chl a' in Chl a-type PS I, and Chl d' in Chl d-type PS I, function as the special pairs, either as homodimers, (BChl a')(2) and (BChl g')(2) in anoxygenic organisms, or heterodimers, Chl a/a' and Chl d/d' in oxygenic photosynthesis. Conversions of BChl g to Chl a and Chl a to Chl d take place spontaneously under mild condition in vitro.

Unique photosystems in Acaryochloris marina.

A short overview is given on the discovery of the chlorophyll d-dominated cyanobacterium Acaryochloris marina and the minor pigments that function as key components therein. In photosystem I, chlorophyll d', chlorophyll a, and phylloquinone function as the primary electron donor, the primary electron acceptor and the secondary electron acceptor, respectively. In photosystem II, pheophytin a serves as the primary electron acceptor.