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1 Polish Journal of Chemistry

1 2002

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The Study of Conformational Equilibrium of c[Gln-Trp-Phe-Gly-Leu-Met], a NK-2 Tachykinin Antagonist

Brzozowski K., Łęgowska A., Rodziewicz-Motowidło S., Liwo A., Rolka K.

Polish Journal of Chemistry

2002

Vol. 76 / nr 6

807-814

Conformational studies of NK-2 tachykinin antagonist c[Gln-Trp-Phe-Gly-Leu-Met] were performed using a combination of two-dimensional NMR spectroscopy and theoretical methods. The three dimensional structure of the peptide studied was determined by global conformational search, using the EDMC method with the ECEPP/3 force field and subsequent calculation of statistical weights of the obtained conformations by fitting the theoretical NOESY spectra and vicinal coupling constants 3JNHH_ to the experimental ones. Using this approach, a set of six conformations with statistical weights higher than 3% was obtained. The first two ones with the values of statistical weights over 30% can be considered as dominant ones. The structure of the most populated conformation is stabilized by type IV _-turn around Trp7-Phe8 and a _-turn centered at Trp7. In the second one, two _ turns were found: II and III_ around Met11-Gln6 and Gln6-Trp7, respectively. In both conformations, the aromatic groups of Trp7 and Phe8 are almost perpendicularly oriented to the peptide backbone. The results obtained correlate well with those published for the peptide studied by three other groups. In contrast to the results obtained by other groups, which used interproton distances as constrains, the approach described here enables to determine the conformational equilibrium of the peptide studied.