Abstract
The thallium-205 chemical shift was determined as a function of temperature for the thallium(I) complexes of gramicidin A and gramicidin B in 2,2,2-trifluoroethanol. From the difference in magnitude of the induced chemical shift it was determined that gramicidin B does not bind the Tl(I) ion as well as does gramicidin A. This result may explain the lower single-channel conductance of gramicidin B relative to gramicidin A. Cabon-13 NMR studies strongly indicate that the binding site for gramicidin A and B is at teh tryptophan end of the molecule and that replacement of tryptophan residue at position 11 in gramicidin A with a phenylalanine to form gramicidin B produces a significant structural change at the tryptophan end of the molecule, but has little effect on the N-terminus.
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