These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Solvent isotope effect on the dark adaptation of bacteriorhodopsin in purple membrane: viewpoints of kinetics and thermodynamics.
    Author: Chiang HK, Chu LK.
    Journal: J Phys Chem B; 2014 Mar 13; 118(10):2662-9. PubMed ID: 24533671.
    Abstract:
    The thermal retinal isomerization from all-trans, 15-anti to 13-cis, 15-syn of bacteriorhodopsin in purple membrane in H2O and D2O during dark adaptation was investigated at 30-55 °C at neutral pH. In this temperature range, phase transition of purple membrane and destruction of the tertiary structure of bacteriorhodopsin did not take place. We found that the solvent isotope effect is inverted below about 45 °C; i.e., k(f)(D2O)/k(f)(H2O) > 1. Applying the transition state theory, the changes in enthalpy from the initial state to the transition state along the thermal trans-to-cis forward reaction coordinate, ΔH(f)*, were determined to be 24.7 ± 1.2 and 20.1 ± 0.4 kcal mol(-1) in H2O and D2O, respectively. The relative entropic change of the transition state in H2O and D2O, ΔΔS(f)* = ΔS(f)*(D2O) - ΔS(f)*(H2O), was -14.4 ± 3.9 cal mol(-1) K(-1). In addition, the Gibbs free energy of trans-to-cis thermal isomerization reaction in D2O is 0.4-0.7 kcal mol(-1) lower than that in H2O. It is the first time the entropy and enthalpy of the transition state have been quantified to elucidate the solvent isotope effect in the retinal thermal isomerization of bacteriorhodopsin during dark adaptation. The solvent isotope effect on the thermodynamics properties and kinetics implied that the hydrogen bonding in the transition state during the dark adaptation of bR is stronger than that in the initial state.
    [Abstract] [Full Text] [Related] [New Search]