Nitrogen-15 nuclear magnetic resonance of aliphatic tripeptides.

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Abstract
The 15N chemical shifts of 8 aliphatic tripeptides were measured at the natural-abundance level. For a given tripeptide, the resonances of the COOH-terminal and NH2-terminal amino acids can be identified by measurements at low or high pH. The shifts of the NH2-terminal amino acid N are essentially independent of the amino acids in the rest of the peptide. The shifts of the other N are characteristic of the amino acids themselves and of the immediately preceding amino acid toward the NH2 terminus. Nonterminal amide N have shifts of about 6 ppm upfield of COOH-terminal amide N at the isoelectric point of measurement. 15N chemical shifts appear to have considerable potential value for peptide sequencing.