Evidence from 13 C solid‐state NMR spectroscopy for a lamella structure in an alanine–glycine copolypeptide: A model for the crystalline domain of Bombyx mori silk fiber

13 C high‐resolution solid‐state NMR coupled with selective 13 C isotope‐labeling of different Ala one methyl carbons was used to clarify the structure of (AG) 15 peptide in the silk II structure as a model for the crystalline domain of Bombyx mori silk fiber. At the inner part of the peptide, the fraction of the peak at 16.6 ppm of the Ala Cβ resonance assigned to β‐turn structure increased at 11th and 19th positions. These data indicate the appearance of the most probable lamellar structure having a turn structure at these two positions, although the position of turn was distributed along the chain.