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: The permeation properties of small organic cations in gramicidin A channels.
    Author: Seoh SA, Busath D.
    Journal: Biophys J; 1993 Apr; 64(4):1017-28. PubMed ID: 7684267.
    Abstract:
    The conductance properties of organic cations in single gramicidin A channels were studied using planar lipid bilayers. From measurements at 10 mM and at 27 mV the overall selectivity sequence was found to be NH4+ > K+ > hydrazinium > formamidinium > Na+ > methylammonium, which corresponds to Eisenman polyatomic cation sequence X'. Methylammonium and formamidinium exhibit self block, suggesting multiple occupancy and single filing. Formamidinium has an apparent dissociation constant (which is similar to those of alkali metal cations) for the first ion being 22 mM from the Eadie-Hofstee plot (G0 vs. G0/C), 12 mM from the rate constants of a three-step kinetic model. The rate-limiting step for formamidinium is translocation judging from supralinear I-V relations at low concentrations. 1 M formamidinium solutions yields exceptionally long single channel lifetimes, 20-fold longer than methylammonium, which yields lifetimes similar to those found with alkali metal cations. The average lifetime in formamidinium solution significantly decreases with increasing voltage up to 100 mV but is relatively voltage independent between 100 and 200 mV. At lower voltages (< or = 100 mV), the temperature and concentration dependences of the average lifetime of formamidinium were steep. At very low salt concentrations (0.01 M, 100 mV), there was no significant difference in average lifetime from that formed with 0.01 M methylammonium or hydrazinium. We conclude that formamidinium very effectively stabilizes the dimeric channel while inside the channel and speculate that it does so by affecting tryptophan-reorientation or tryptophan-lipid interactions at binding sites.
    [Abstract] [Full Text] [Related] [New Search]