Crystallization of macromolecular heparin.

X-ray fibre-diffraction photographs were obtained from oriented films of the sodium salt of macromolecular heparin (molecular weight approx. 10(6)) prepared from rat skin. Two distinct molecular chain conformations corresponding to two different crystal lattices were observed as a function of relative humidity. The first conformation, obtained at 78% relative humidity, has a layer-line spacing of 1.73nm, which can be interpreted as an approximate twofold helix. On increasing the relative humidity to 84% a second phase with a layer-line repeat of 1.65nm is obtained with the reflexions indexing on a triclinic unit cell similar to that obtained previously (Nieduszynski & Atkins, 1973) for pig mucosal heparin.