CHARACTERIZATION OF THE RHODOCYCLUS-TENUIS PHOTOSYNTHETIC REACTION-CENTER

The photosynthetic reaction center (RC) from the purple non sulfur bac terium Rhodocyclus tenuis was isolated from membrane fragments by dode cyl dimethylamine oxide (LDAO) and purified by DEAE-chromatography in presence of dodecyl-maltoside (DM), The redox midpoint potential of th e primary electron donor P was determined to be E-m = 515 mV +/- 20 mV . The P+ absorption band peaks at 1260 nm. Fourier transform resonance Raman spectra are consistent with a dimeric (Bchl)(2) structure of P where both acetyl carbonyl groups of P are hydrogen bonded, one with h istidine, the other with a tyrosine residue. The primary quinone (Q(A) ) was identified to be menaquinone 8 and the secondary one (Q(B)) ubiq uinone b. The secondary-activity depends on the nature of the detergen t. At pH 8 in DM solution, the rate of the P(+)Q(B)(-) back reaction i s 0.1 s(-1) and Q(B) does not function as a two-electron gate. With LD AO addition, the rate became 0.3 s(-1) and multiple binary oscillation s of Q(B)(-) were observed. 10 mu M orthophenanthroline blocks 50% of the electron transfer to Q(B) (I-50 = 10 mu M). This high sensitivity was correlated with the nature of the residue at the position L226. (C ) 1997 Elsevier Science B.V.