Abstract

The photosynthetic reaction center (RC) from the purple bacterium Rb. sphaeroides is a member of the closely related family of light harvesting membrane proteins that are responsible for carrying on photosynthesis in nature. The two C2 symmetry related subunits, L and M, consist of transmembrane alpha helixes and eight cofactors [4 Bacteriochlorophylls (Bchl), 2 Bacteriopheophytins (Bph) and 2 Ubiquinones (Q)]. The cofactors are arranged in a wishbone geometry, with a dimerized pair of bacteriochlorophylls at the center (also called the 'special pair', P), and one each of Bchl, Bph and Q (in that order) along each side of the wishbone. The primary events of photosynthesis consist of the formation of the excited singlet state P* of the dimer by the absorption of a near infrared (NIR) photon by P, and subsequent transfer of an electron to the Bph on the L side with a time constant of ca 3ps forming P⁺Bph⁻. The role of the L side Bchl in this process is uncertain.

© 1994 Optical Society of America