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Electrochemical redox titration of cofactors in the reaction center from Rhodobacter sphaeroides
Author(s) -
Moss D.A.,
Leonhard M.,
Bauscher M.,
Mäntele W.
Publication year - 1991
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(91)80547-g
Subject(s) - rhodobacter sphaeroides , redox , photosynthetic reaction centre , chemistry , redox titration , cofactor , rhodospirillaceae , electrochemistry , titration , rhodospirillales , rhodobacter , photochemistry , inorganic chemistry , biochemistry , photosynthesis , electron transfer , electrode , enzyme , mutant , gene
The electrochemical redox poising of the primary electron donor P and of the quinone electron acceptor(s) Q in isolated reaction centers from Rhodobacter sphaeroides in an ultra‐thin‐layer electrochemical cell, monitored by chronoamperometry and by spectroscopy in the visible/near‐infrared region, is reported. Electrical application of a redox potential of +0.4 V (vs. Ag/AgCl/3 M KCl) leads to quantitative formation of the π‐cation radical of P within a few minutes. The oxidized product can be re‐reduced to the neutral species by application of 0 V, and full reversibility is maintained over many‐cycles. By poising at a series of intermediate potentials, a titration curve for the 865 nm P band was obtained, which could be fitted to a Nernst function with E m = 0.485 vs. SHE and n = 0.96. By Application of negative potentials (−0.2 V and −0.45 V vs. Ag/AgCl/3 M KCl), the quinone electron acceptors were reversibly reduced as demonstrated by the shift of bacteriopheophytin absorption and drastically changed kinetics of charge recombination. The use of this thin‐layer electrochemical technique for the determination of midpoint potentials, for the investigation of redox‐poised electron transfer reactions as well as for spectroscopy in the mid‐infrared region is discussed.