Heterogeneous exchange behavior of Samia cynthia ricini silk fibroin during helix–coil transition studied with 13C NMR

Abstract
The structure and structural transition of the glycine residue adjacent to the N-terminal alanine residue of the poly(L-alanine), (Ala)12–13, region in Samia cynthia ricini silk fibroin was studied using 13C nuclear magnetic resonance (NMR). Most of the glycine carbonyl peaks in the 13C solution NMR spectrum of [1-13C]glycine-silk fibroin could be assigned to the primary structure from the comparison of the 13C chemical shifts of seven glycine-containing tripeptides. The slow exchange between helix and coil forms in the NMR time scale was observed with increasing temperature exclusively for the underlined glycine residue in the Gly-Gly-(Ala)12–13 sequence during fast helix–coil transition of the (Ala)12–13 region

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