ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
An X-ray study has been made of the synthetic polypeptide poly-L-ornithine hydrobromide to investigate whether, like the chemically related polypeptides poly-L-lysine and poly-L-arginine hydrochlorides, it can undergo conformational changes merely from variations in its degree of hydration. X-ray powder and fiber photographs of specimens with from half up to about three molecules of water per ornithine residue show features that suggest a “cross-β-pleated-sheet” structure. Each pleated sheet is formed from parallel chains and the sheets are piled up along the b axis. The spacings, which do not vary appreciably with hydration, can be satisfactorily indexed in terms of an orthogonal unit cell with a = 4.60 Å, b = 30.2 Å, and c = 6.64 Å. These dimensions are shown by models to be compatible with the proposed structure. Removal of the last half molecule of water results in a very diffuse pattern but on rehydration the sharp pattern reappears. Specimens containing four to nine molecules of water per residue show a quite different pattern. Reflections other than equatorial are absent in oriented diagrams except for a 5.4 Å diffuse streak across the meridian which is suggestive of an α-helical structure. Increasing the relative humidity from 86% to about 100% causes the a axis of the hexagonal unit cell to increase from 14.7 Å to 15.3 Å. On drying, the β structure reappears once again. These conformational changes are very similar to those observed in poly-L-lysine hydrochloride except that the latter shows a more stable α-helical form. This difference may be explained in terms of stabilizing hydrophobic interactions between side chains, since ornithine has a shorter side chain than lysine.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.1973.360120907
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