U. Shmueli, W. Traub
May 1, 1965
Citations
0
Influential Citations
50
Citations
Journal
Journal of molecular biology
Abstract
Poly- L -lysine hydrochloride is a water-soluble synthetic polypeptide which resembles basic proteins in some of its properties. Its molecular structure, at various degrees of hydration, has been investigated with the aid of X-ray diffraction photographs of powder and oriented fibre specimens. Dry polylysine hydrochloride has a pleated-sheet structure characteristic of β -polypeptides. Increasing relative humidity causes a gradual expansion in the intersheet spacing from 15·2 A at 0% relative humidity to 17·0 A at 84% relative humidity, at which point approximately the pleated sheets break up with the formation of α -helices. The hexagonal array of a-helices is able to expand evenly and thus accommodate still more water, but by about 15 molecules of water per residvie of lysine hydrochloride the crystalline packing disappears. In dilute solution the polymer assumes a random-coil form. All these structural changes can be reversed by drying. The various structures are stabilized mainly by ionic forces, and the transformations can be explained in terms of increased mobility of the chloride ions with increased hydration.