Some New Investigations on the Structure of Synthetic Polypeptides

• Published in: Proceedings of the Royal Society of London. Series B, Biological sciences Biological sciences, 1953-03, Vol.141 (902), p.49-59
• Main Authors: Bamford, C. H., Brown, L., Elliott, A., Hanby, W. E., Trotter, I. F.
• Format: Article
• Language: English
• Subjects: A Discussion on the Structure of Proteins; Amides; Crystal structure; Crystallinity; Crystallites; Crystals; Density; Dichroism; Molecules; Old Medline; Peptides; Polymers; X ray film
• ISSN: 0962-8452; 0080-4649; 0950-1193; 2053-9193; 1471-2954; 2053-9193
• DOI: 10.1098/rspb.1953.0016

Films of $\text{poly}$-$\gamma $-$\text{methyl-L-glutamate}$ have been prepared with a high degree of orientation, X-ray photographs show that the least dimensions of the unit cell are $a$ = 11.95 angstrom, $b$ = 20.70 angstrom, $c$ = 43.2 angstrom $\text{(fibre axis)}$. One near-meridional reflexion, if produced by the same crystalline phase, requires doubling of the length of the c-axis. If all the observed reflexions arise from a single phase, no structure hitherto proposed for the $\alpha $-$\text{fold}$ will completely explain the intensities. However, the general pattern of intensities of non-meridional reflexions is in at least qualitative agreement with that calculated by Cochran & Crick for the $\alpha $-$\text{helix}$. The significance of the infra-red dichroism of polypeptides is discussed, and compared with the dichroism observed in the $C=O$ stretching band in acetanilide. Measurements of the density of $\text{poly}$-$\gamma $-$\text{methyl-L-glutamate}$ are reported, and compared with the value calculated on the $\alpha $-$\text{helix}$ model.