Isotope effect on electron transfer in reaction centers from Rhodopseudomonas sphaeroides
AUTOR(ES)
Okamura, M. Y.
RESUMO
Previous ENDOR studies on reaction centers from Rhodopseudomonas sphaeroides have shown the presence of two hydrogen-bonded protons associated with the primary, ubiquinone, acceptor QA. These protons exchange with deuterons from solvent 2H2O. The effect of this deuterium substitution on the charge-recombination kinetics (BChl)2+QA- → (BChl)2QA has been studied with a sensitive kinetic difference technique. The electron-transfer rate was found to increase with deuterium exchange up to a maximum Δk/k of 5.7 ± 0.3%. The change in rate was found to have an exchange time of 2 hr, which matched the disappearance of the ENDOR lines due to the exchangeable protons. These results indicate that these protons play a role in the vibronic coupling associated with electron transfer. A simple model for the isotope effect on electron transfer predicts a maximum rate increase of 20%, which is consistent with the experimental results.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=386885Documentos Relacionados
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