Proton spin-lattice relaxation studies of [D-Ala2-Met5]enkephalin

Application of selective and nonselective proton relaxation rate measurements to molecules outside the ω02tc2 « 1 limit is explored using [D-Ala2-Met5]enkephalin. Monoselective, biselective, and nonselective measurements yielded cross-relaxation rates, σ, and F ratios; from these, it was deduced that enkephalin has a relatively rigid backbone, internal motion of the Ala2, Phe4, and Met5 side chains, a small reorientation of the Tyr1 aromatic ring, and proximity of the Ala2 and Met5 methyl groups. These data support but do not prove the existence of the β-turn conformations. All proton relaxation is dominated by dipolar mechanisms. © 1980, American Chemical Society. All rights reserved.