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The Structure of Synthetic Polypeptides. I. X-Ray Investigation

C. H. Bamford, W. E. Hanby and F. Happey
Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences
Vol. 205, No. 1080 (Jan. 22, 1951), pp. 30-47
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/98721
Page Count: 20
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The Structure of Synthetic Polypeptides. I. X-Ray Investigation
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Abstract

Oriented fibres and films of a number of synthetic polypeptides have been prepared, and examined by X-ray diffraction. It is shown that the polypeptides can exist in a folded (α ) and an extended (β ) configuration. The observations on the α form are consistent with the presence of a twofold screw axis in symmetrical polypeptides, and lead to a value of about 5· 5 Å for the true fibre repeat distance. The fibre period in the copolymers is shown to be greater than 5· 26 Å. It is considered that the X-ray evidence favours a ribbon-like molecule, in agreement with the structure shown in I. The β forms of the polypeptides give X-ray diagrams similar to those of β proteins, and probably consist of extended polypeptide chains. It is shown that the polypeptides can undergo an $\alpha \rightleftarrows \beta $ transformation similar to that encountered in the fibrous α proteins. The medium from which the peptide is regenerated has a very important influence in determining which form is obtained. Formic acid appears to be unique in producing the β modification of polypeptides which swell or dissolve in this liquid. A mechanism for this transformation is suggested. A number of copolymers containing glycine have been examined. These appear to exist mainly in the β form. The similarities in the behaviour of synthetic polypeptides and fibrous proteins are discussed.

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