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X-Ray Studies of Nucleic Acids. 1947.

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Title:	X-Ray Studies of Nucleic Acids [6 of 13]
Creator:	Astbury, William
Contributor:	Symposia of the Society for Experimental Biology, No. 1
Publisher:
Date:	1947-00-00
Subject:	Nucleic acids -- Structure X-rays -- Diffraction
Description:	Symposia of the Society for Experimental Biology, No. 1
Type:	Text
Format:	text/plain
Language:	en
Identifier:	astbury-pg06
Source:	Master scanned with Epson GT-10000+ flatbed scanner at 600 dpi.
Rights:	http://osulibrary.orst.edu/specialcollections/coll/pauling/dna/copyright.html
Full Text:	" X-RAY STUDIES OF NUCLEIC ACIDS 7I place-except, of course, that it is a lateral shrinkage. We obtained a similar result when we tried the experiment of spinning very fine fibres into warm alcohol by means of a spinneret. Some of these fibres were as fine as spider's web and we hoped that they would give a perfectly oriented X-ray diagram; but owing to the strong dehydrating action of the warm alcohol the photograph turned out to be one of the poorest we had ever obtained. It is evident that water molecules play an essential part in the stability of the crystalline aggregates built up by Na thymonucleate at ordinary humidity, in which respect they resemble the crystallites of alginic acid (Astbury, 1945 b). Pl. I, figs. 2a and 2b show two hitherto unpublished X-ray comparison photographs of oriented Na thymonucleate and an oriented preparation of the tough fibrous compound that, following advice from Dr Albert Fischer of the Carlsberg Foundation, we made by interaction between an aqueous, Na thymonucleate solution and a hydrochloric acid solution of the pro- tamine, clupein. If the idea is sound that this interaction can take place without steric hindrance by fitting column and chain directly alongside each other, we might expect a strong meridian are at 3-31 A. to dominate the fibre diagram of clupein thymonucleate just as it does that of the sodium compound, though there should be increases in the side spacings. Figs. 2a and 2b show how these expectations appear to be justified: the principal intramoleeular period along the fibre axis, the period that is common to nucleotides and side chains alike, remains unchanged. Dr K. Bailey kindly carried out for us some chemical analyses of this compound of clupein and thymonucleic acid and found the following: phosphorus, 5-65°0; nitrogen, 21-8°,,''; ash, 1-8°,0. These figures lead to about 57 0/,0 thymonucleic acid, and 41 °:',0 clupein, by weight. Now accord- ing to Linderstrom-Lang (1935) and Rasmussen & Linderstrom-Lang (1935) the clupein chain consists of some 2o arginine residues and 8 mono- amino (or imino) residues, weighing in all about 4000, leading to an average residue weight of about 143; while according to `1"aldsclunidt-Leitz and coworkers (Waldschinidt-Leitz & Kofranyi, 1935) it consists of 1o arginine residues and 5 monoamino (or imino) residues, weighing in all 2021, leading to an average residue weight of about 135. On the basis, therefore, of the Linderstrom-Lang figures it follows that our clupein thymonucleate is composed of amino acid residues and nucleotides in the ratio (41 x 308) : (57 x 143), i.e. about 1-55 : I ; while on the basis of the `'Valdschmidt-Leitz figures the corresponding ratio is about 1-64: 1. For strict chemical equivalence between the phosphoric acid groups of the nucleotides and the basic side chains of the protein we should expect 28:20, i.e. 1-:}: 1, from the Linderstrom-Lang figures, and i5: Io, i.e.