Crystallization of macromolecular heparin (Short Communication)

X-ray fibre-diffraction photographs were obtained from oriented films of the sodium salt of macromolecular heparin (molecular weight approx. 10⁶) 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.