D-H Exchange During Collagen-Fold Formation. Nucleation Processest

Abstract

Nucleation of collagen-fold formation has been followed by D-H exchange techniques coupled with infra-red measurements of the Arnide II absorbance at 1550 cm-'. Solution Sephadex exchange and thin film exchange techniques were applied to two gelatin fractions differing in molecular weight and chain cross-linking. The exchange rate was measured at temperatures, T above and below the melting temperature, TM. At T> TM two classes of exchangeable H were detected. On the basis of their pD-rate profiles, these classes were assigned to pyrollidine ring rich chain sequences and t o the sequences deficient in these residues. At T< TM two additional classes were noted -a non-exchangeable group (the fold-nuclei) and a restricted exchange group probably adjacent to the fold-nuclei. It is proposed that nucleation begins in the pyrollidine residue rich regions but that there is a preliminary H-bonding in regions adjacent to the nuclei which must be reorganized before collagen-fold growth is propagated. Molecular weight...