An NMR Study of the Conformations of N-terminal Substance P Fragments and Antagonists

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Abstract
Three N-terminal fragments of the neurotransmitter Substance P as well as two antagonist heptapeptides containing D-amino-acid residues were studied using different ID and 2D NMR techniques. Total nonexchangeable 1H-NMR assignments were carried out in D2O and the NH protons were assigned in H2O by means of COSY experiments. The spectral data indicates that there are no preferred conformations for the backbone. The N-terminal tetrapeptide SP1–4-OH exists as a mixture of cis/trans isomers and this effect was studied as a function of pH.