Deuterium–Hydrogen Exchange of Collagen Like Synthetic Polypeptides

Abstract

THE two models of collagen structure which have been developed since 1954 have been confirmed by X-ray diffraction studies of the collagen fibres. Both models are similar, the chief difference being in the number of hydrogen bonds. Rich and Crick¹ assumed that there was one hydrogen bond for each tripeptide unit (one bonded structure) while Ramachandran² assumed two hydrogen bonds per unit (two bonded structure) in the structure he suggested. Thus differences in the sequence of the amino-acids and changes in the position of atoms are unavoidable. In the collagen structure II of Rich and Crick, position 1 of the tripeptide unit is always occupied by a glycine unit; the positions 2 and 3 may be occupied by any other amino-acid including proline and hydroxyproline. On the other hand, in the Ramachandran structure an imino-acid unit can only occupy position 3 if changes in the collagen structure are to be avoided. The results obtained by Harrington³ and Bensusan and Nielsen⁴ support the structure proposed by Ramachandran. Investigations into synthetic polypeptides composed of tripeptide units, such as gly-pro-hypro^5,6 and pro-gly-pro⁷, have shown that only one hydrogen bond per tripeptide unit is sufficient for the formation of a collagen like structure in solution as well as in the solid state.