HETEROGENEITY OF THE QUINONE ELECTRON-ACCEPTOR SYSTEM IN BACTERIAL REACTION CENTERS

BACIOU L SEBBAN P

L. Baciou et P. Sebban, HETEROGENEITY OF THE QUINONE ELECTRON-ACCEPTOR SYSTEM IN BACTERIAL REACTION CENTERS, Photochemistry and photobiology, 62(2), 1995, pp. 271-278

36

INGLESE

Article

Biophysics,Biology

Photochemistry and photobiology → ACNP

0031-8655

62

2

1995

271 - 278

ISI

0031-8655(1995)62:2<271:HOTQES>2.0.ZU;2-O

In reaction centers from Rhodopseudomonas viridis, biphasicity of the charge recombination kinetics between P+, the primary electron donor, and Q(A)(-) and Q(B)-, the primary and secondary quinone electron acce pters, respectively, have been analyzed by the flash-induced absorptio n change technique. We have studied the effect of quinone environment modifications on the ratio of the two phases for the P(+)Q(A)(-) ([A(f ast)/A(slow)](a)) and P(+)Q(B)(-) ([A(fast)/A(slow)](b)) charge recomb ination processes. In reaction centers from Rps. viridis reconstituted in phosphatidylcholine liposomes a notable influence of the nature of the Q(B) pocket occupancy was observed on (A(fast)/A(slow))(a). This ratio is much affected by the presence of o-phenanthroline compared to reaction centers with an empty Q(B) pocket or with terbutryn present. Because o-phenanthroline was proposed to hydrogen bind His(L190), whe reas terbutryn does not, we suggest that a His(L190)-Fe-His(M217) (the equivalent to His(L190) in, the Q(A) pocket) ''wire'' may be involved in the existence of the two conformational states associated with the two phases of charge recombination. In chromatophores from the T-1 (S er(L223) --> Ala; Arg(L217) --> His) and T-4 (Tyr(L222) --> Phe) mutan ts no modification of the (A(fast)/A(slow))(a) ratio is detected, wher eas the (A(fast)/A(slow))(b) ratios are substantially modified compare d to the wild type (WT), In the T-3 mutant (Phe(L216) --> Ser; Val(M26 3) --> Phe [4.1 Angstrom apart from Q(A)]), (A(fast)/A(slow))(a) is no tably changed compared to the WT. Our data show that any modification in the close protein environment of the quinones and/or of the His(L19 0) and His(M217) affects the equilibrium between the two reaction cent er states. This is consistent with the existence of two reaction cente r states from Rps. viridis, associated with two different conformation s of the quinones-histidines-iron system. This ''wire'' allows both qu inone protein pockets to interact over quite long distances.