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ull is considered to be useful for the study on the manner of the hydrogen bonding of polypeptides and proteins. (21) Harbison, G. S.; Jelinski, L. W.; Stark, R. E.; Torchia, D. A.; Herzfeld, J.; Griffin, R. G. J. Magn. Reson. 1984, 60, 79-82.

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Three kinds of 2H-labeled Bombyx mori silk fibroin samples (with [2,2-2H2]Gly, [3,3,3-2H3]Ala, or [2,3,5,6-2H4]Tyr) were obtained by oral administration of either the labeled amino acid or 2H2O to 5th instar larvae. The administration of 2H2O alone yielded a high degree of selective deuteration at the alanine methyl group, since the incorporation of 2H2O occurs between fumarate and malate in the tricarboxylic acid (TCA) cycle of the silk fibroin synthetic pathway. Uniaxially oriented silk fibers were prepared as samples for 2H-NMR spectroscopy. An analysis of the quadrupole echo line shape was carried out in order to determine the angle of the deuterium-labeled group relative to the fiber axis, i.e., of the Cα−2H bond vectors in glycine and of Cα−Cβ2H3 in alanine. With the fiber axis aligned parallel to the magnetic field, quadrupole splittings were obtained as 117.8 and 39.8 kHz for [2,2-2H2]Gly- and [3,3,3-2H3]Ala-labeled silk, respectively. These values are identical with those obtained from the 2H-NMR powder patterns of the unaligned samples, within experimental error. From the angular dependence of the quadrupole splittings, it was thus calculated that the Cα−2H bonds of glycine as well as the Cα−Cβ2H3 bond of alanine make an angle of approximately 90° relative to the fiber axis. These steric constraints were then used to evaluate the torsion angles, φ and ψ, for the glycine and alanine residues within the protein backbone. These data, determined independently by solid-state 2H NMR, thus verified and narrowed down the allowed region in the Ramachandran (φ, ψ) map obtained from previous solid-state 13C- and 15N-NMR studies.

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