Conformation of GABA-5-enkephalinamide in water solution: carbon-13 and proton NMR study.

13C and 1H magnetic resonances of g-aminobutyric acid-5 enkephalinamide [84244-52-0] were assigned in water by selective decoupling, spectral analyses, pD titrns., and literature data. The anal. of chem. shifts, coupling consts., and rotamer populations around c1 suggested a high pH-induced conformational transition at the N-terminus of the peptide corresponding to some rearrangement of tyrosine-1, glycine-2, and glycine-3 residues. Phenylalanine-4 and GABA-5 were not affected by this conformational transition. The conformational nature of both cationic and neutral forms seemed to exclude the presence of intramol. bends and favored an extended form. This conclusion was supported by the temp. coeffs. of the amino acid a-carbons and by theor. conformational calcns.