Photosystem I and II reaction centers of a new oxygenic organism Acaryochloris marina that use chlorophyll d.

Abstract

PS I and II reaction centers of a cyanobacteria-like oxygenic organism Acaryochloris marina were studied. The organism has chlorophyll d (Chl d) that has a formyl group on chlorin ring and absorbs at 700-720 nm and Chl a in a molar ratio of 30:1. Isolated PS I contains one special pair of Chl d (P740), which shows an absorption change at 740 nm and has Em of +335 mV, in 145 chlorophyll d on RC polypeptides homologous to cyanobacteria1. Laser spectroscopy, ENDOR and FTIR studies indicated the structure and environments of P740 similar to but somewhat different from those of Chl a dimer P700. Electron acceptor phylloquinone was extracted with diethyl ether and its function was replaced by reconstituted artificial quinones. Absorption changes of Chls in PS II were also studied in isolated thylakoids after chemical oxidation of P740. The difference spectrum gave a peak at 720 nm with no peak at 680 nm suggesting PS II special pair of this organism to be Chl d. 1Q. Hu, H. Miyashita, I. Iwasaki, K. N. Kurano, S. Miyachi, M. Iwaki and S. Itoh, Proc. Natl. Acad. Sci., 95, 13319 (1998).