PMID- 9129834
OWN - NLM
STAT- MEDLINE
DCOM- 19970630
LR  - 20181113
IS  - 0006-3495 (Print)
IS  - 1542-0086 (Electronic)
IS  - 0006-3495 (Linking)
VI  - 72
IP  - 5
DP  - 1997 May
TI  - The interaction of quinone and detergent with reaction centers of purple 
      bacteria. I. Slow quinone exchange between reaction center micelles and pure 
      detergent micelles.
PG  - 2304-19
AB  - The kinetics of light-induced electron transfer in reaction centers (RCs) from 
      the purple photosynthetic bacterium Rhodobacter sphaeroides were studied in the 
      presence of the detergent lauryldimethylamine-N-oxide (LDAO). After the 
      light-induced electron transfer from the primary donor (P) to the acceptor 
      quinone complex, the dark re-reduction of P+ reflects recombination from the 
      reduced acceptor quinones, QA- or QB-. The secondary quinone, QB, which is 
      loosely bound to the RC, determines the rate of this process. Electron transfer 
      to QB slows down the return of the electron to P+, giving rise to a slow phase of 
      the recovery kinetics with time tau P approximately 1 s, whereas charge 
      recombination in RCs lacking QB generates a fast phase with time tau AP 
      approximately 0.1 s. The amount of quinone bound to RC micelles can be reduced by 
      increasing the detergent concentration. The characteristic time of the slow 
      component of P+ dark relaxation, observed at low quinone content per RC micelle 
      (at high detergent concentration), is about 1.2-1.5 s, in sharp contrast to 
      expectations from previous models, according to which the time of the slow 
      component should approach the time of the fast component (about 0.1 s) when the 
      quinone concentration approaches zero. To account for this large discrepancy, a 
      new quantitative approach has been developed to analyze the kinetics of electron 
      transfer in isolated RCs with the following key features: 1) The exchange of 
      quinone between different micelles (RC and detergent micelles) occurs more slowly 
      than electron transfer from QB- to P+; 2) The exchange of quinone between the 
      detergent "phase" and the QB binding site within the same RC micelle is much 
      faster than electron transfer between QA- and P+; 3) The time of the slow 
      component of P+ dark relaxation is determined by (n) > or = 1, the average number 
      of quinones in RC micelles, calculated only for those RC micelles that have at 
      least one quinone per RC (in excess of QA). An analytical function is derived 
      that relates the time of the slow component of P+ relaxation, tau P, and the 
      relative amplitude of the slow phase. This provides a useful means of determining 
      the true equilibrium constant of electron transfer between QA and QB (LAB), and 
      the association equilibrium constant of quinone binding at the QB site (KQ+). We 
      found that LAB = 22 +/- 3 and KQ = 0.6 +/- 0.2 at pH 7.5. The analysis shows that 
      saturation of the QB binding site in detergent-solubilized RCs is difficult to 
      achieve with hydrophobic quinones. This has important implications for the 
      interpretation of apparent dependencies of QB function on environmental 
      parameters (e.g. pH) and on mutational alterations. The model accounts for the 
      effects of detergent and quinone concentration on electron transfer in the 
      acceptor quinone complex, and the conclusions are of general significance for the 
      study of quinone-binding membrane proteins in detergent solutions.
FAU - Shinkarev, V P
AU  - Shinkarev VP
AD  - Department of Plant Biology, University of Illinois, Urbana 61801-3837, USA.
FAU - Wraight, C A
AU  - Wraight CA
LA  - eng
PT  - Journal Article
PT  - Research Support, U.S. Gov't, Non-P.H.S.
PL  - United States
TA  - Biophys J
JT  - Biophysical journal
JID - 0370626
RN  - 0 (Benzoquinones)
RN  - 0 (Detergents)
RN  - 0 (Dimethylamines)
RN  - 0 (Micelles)
RN  - 0 (Photosynthetic Reaction Center Complex Proteins)
RN  - 3T006GV98U (quinone)
RN  - 4F6FC4MI8W (dodecyldimethylamine oxide)
SB  - IM
MH  - Benzoquinones/*metabolism
MH  - Detergents/*pharmacology
MH  - Dimethylamines/*pharmacology
MH  - Kinetics
MH  - Micelles
MH  - Models, Chemical
MH  - Photosynthetic Reaction Center Complex Proteins/*metabolism
MH  - Rhodobacter sphaeroides
PMC - PMC1184426
EDAT- 1997/05/01 00:00
MHDA- 1997/05/01 00:01
PMCR- 1998/05/01
CRDT- 1997/05/01 00:00
PHST- 1997/05/01 00:00 [pubmed]
PHST- 1997/05/01 00:01 [medline]
PHST- 1997/05/01 00:00 [entrez]
PHST- 1998/05/01 00:00 [pmc-release]
AID - S0006-3495(97)78875-1 [pii]
AID - 10.1016/S0006-3495(97)78875-1 [doi]
PST - ppublish
SO  - Biophys J. 1997 May;72(5):2304-19. doi: 10.1016/S0006-3495(97)78875-1.