The antenna reaction center complex of heliobacteria: composition, energy conversion and electron transfer

A survey is given of various aspects of the photosynthetic processes in hel iobacteria. The review mainly refers to results obtained since 1995, which had not been covered earlier. It first discusses the antenna organization a nd pigmentation. The pigments of heliobacteria include some unusual species : bacteriochlorophyll (BChl) g, the main pigment, 8(1) hydroxy chlorophyll a, which acts as primary electron acceptor, and 4,4'-diaponeurosporene, a c arotenoid with 30 carbon atoms. Energy conversion within the antenna is ver y fast: at room temperature thermal equilibrium among the approx. 35 BChls g of the antenna is largely completed within a few ps. This is then followe d by primary charge separation, involving a dimer of BChl g (P798) as donor , but recent evidence indicates that excitation of the acceptor pigment 8(1 ) hydroxy chlorophyll a gives rise to an alternative primary reaction not i nvolving excited P798. The final section of the review concerns secondary e lectron transfer, an area that is relatively poorly known in heliobacteria. (C) 2001 Elsevier Science B.V. All rights reserved.