Evidence from super(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

super(13)C high-resolution solid-state NMR coupled with selective super(13)C isotope-labeling of different Ala one methyl carbons was used to clarify the structure of (AG) sub(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 C beta resonance assigned to beta -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.