ELECTRON-TRANSFER IN MENAQUINONE-DEPLETED MEMBRANES OF HELIOBACTERIUM-CHLORUM

Treatment of membranes of Heliobacterium chlorum with diethyl ether at various levels of water saturation resulted in extraction of bacteriochlorophyll (BChl) g and menaquinones. Only a minor enrichment of P-798 with respect to antenna BChl g could be achieved, whereas menaquinone (vitamin K-2), the only quinone found in this species (Hiraishi, A. (1989) Arch. Microbiol. 151, 378-379), was essentially completely removed. Extraction of menaquinone, however, did not result in significant changes in electron transport. Electron transport to secondary electron acceptors was not impaired by wet ether extraction, either at room temperature or at low temperature. As in intact membranes, radical pair recombination and subsequent triplet formation were only observed under strongly reducing conditions. These results suggest that menaquinone is not an essential participant in the electron acceptor chain of heliobacteria.