PURIFICATION AND CHARACTERIZATION OF REACTION CENTERS FROM THE OBLIGATE AEROBIC PHOTOTROPHIC BACTERIA ERYTHROBACTER-LITORALIS, ERYTHROMONAS-URSINCOLA AND SANDARACINOBACTER-SIBIRICUS

Reaction centers (RC) from the species Erythrobacter (Eb.) litoralis, Erythromonas (Em.) ursincola and Sandaracinobacter (S.) sibiricus have been purified by LDAO treatment of light-harvesting-reaction center c omplexes and DEAE chromatography. The content and overall organisation of the RCs' chromophores, determined by linear dichroism (LD) and abs orption spectroscopy, are similar to those isolated from anaerobic pho tosynthetic bacteria. The redox properties of the primary electron don or are pH-independent and very similar to those determined for anaerob ic photosynthetic bacteria with midpoint potential values equal to 445 (+/- 10), 475 and 510 mV for Eb. litoralis, S. sibiricus and Fm. ursi ncola, respectively. The RC purified from Eb. litoralis does not conta in bound cytochrome (cyt), whereas RCs isolated from S. sibiricus and Fm. ursincola possess a tetraheme cyt c. Each of these tetraheme cyts contains two high potential hemes and two low potential hemes. Their r edox properties-are very similar, with midpoint potentials equal to 38 5 (+/- 10), 305, 40, -40 mV for Fm. ursincola and 355, 285, 30, -48 mV for S. sibiricus. At physiological pH, the midpoint potential of the primary electron acceptor (Q(A)) varies with a slope of -60 mV/pH unit . The reduced form of Q(A) presents pK values of 9, 9.8, 10.5 for S. s ibiricus, Fm. ursincola. and Eb. litoralis, respectively. The main dif ference observed between RCs isolated from anaerobic photosynthetic an d from obligate aerobic bacteria is the E-m values of Q(A) which are 6 5 to 120 mV higher in the last case. This difference is proposed to be a major reason for the inability of these species to grow under anaer obic photosynthetic conditions.