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An ordered precipitate of polyadenylic acid formed by freezing at acidic pH: Comparison of X‐ray diffraction and other properties of the precipitate with those of fibers or direct acid‐precipitates
Author(s) -
Zimmerman Steven B.,
Coleman Norma F.
Publication year - 1972
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1972.360110914
Subject(s) - diffraction , chemistry , solubility , crystallography , fiber diffraction , fiber , x ray crystallography , organic chemistry , optics , physics
Poly A was found to precipitate upon freezing acidic solutions at p H values where it is normally soluble; this precipitate tends to have the form of small thin plates of irregular outline (“plates”). The X‐ray diffraction pattern and solubility properties of the “plates” were compared with those of poly A precipitated solely by exposure to lower p H values, and with fibers drawn from acidic solution. There is considerable molecular order in each of these three types of preparation. In all cases, the diffraction patterns are consistent with the presence of the double‐stranded helical structure proposed by Rich, Davies, Crick, and Watson ( J. Mol. Biol. , 3 , 71 (1961)) based on fiber diffraction data. The diffraction pattern from the “plates” is compared in detail with that of the fibers, and is shown to be in accord with a packing scheme having the chain axis of the molecular structure confined to the plane of the “plate,” but oriented randomly in that plane.