APPLICATION OF THERMOSTABLE REACTION CENTERS FROM CHLOROFLEXUS-AURANTIACUS AS A PROTONMOTIVE FORCE GENERATING-SYSTEM

Reaction centers (RCs) were purified from the thermophilic phototrophi c bacterium Chloroflexus aurantiacus and reconstituted into liposomes. The dependence of cyclic electron transfer via horse-heart cytochrome c, UQ0 and purified or reconstituted RCs on pH, temperature and ionic strength was investigated. The highest rates of photo-oxidation of cy tochrome c were achieved at pH 8 or higher, at 55-degrees-C and at an ionic strength below 5 . 10(-4). RCs solubilized with octyl beta-D-glu coside could be reconstituted by detergent dialysis into liposomes com posed of phospholipids from Escherichia coli or Bacillus stearothermop hilus. Upon illumination of RC-containing liposomes in the presence of horse heart cytochrome c and UQ0 a membrane potential of - 160 mV was generated. Maximal values of a membrane potential were generated at 1 .1 nmol RC/mg phospholipid. RC-containing liposomes were fused with me mbrane vesicles from Clostridium fervidus by a freeze/thaw/sonication method (Driessen et al. (1985) Proc. Natl. Acad. Sci. USA 82, 7555-755 9). In these hybrid membranes a protonmotive force of - 90 mV could be generated upon illumination. The light-induced protonmotive force cou ld drive uptake Of L-Serine into the hybrid membranes. Incorporation o f this thermostable DELTAp-generating system into membrane vesicles fr om bacteria makes it possible to study secondary transport processes u nder anaerobic conditions.