The energy profile and the rate of oxidation of trimethylquinol in a model system including the Fe2S2 cluster of the cytochrome b 6 f complex and the surrounding amino acid residues (Cys134-Thr135-His136-Leu137-Gly138-Cys139, Cys152, Cys154-His155-Gly156-Ser157, Tyr159) were calculated by density functional theory (DFT). The limiting stage of quinol oxidation, namely, the transfer of hydrogen from quinol to the nearest nitrogen atom (His155), was an endoergonic process (ΔE = 10.6 kcal/mol), in which the energy barrier E a = 25.5 kcal/mol had to be overcome. The rate constant for this reaction was evaluated in terms of the Marcus theory using the semiempirical Moser-Dutton equation; the resulting values, k PCET = 40-170s-1, agreed well with the available experimental data.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry