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X-Ray Studies of Nucleic Acids. 1947.

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Title:	X-Ray Studies of Nucleic Acids [10 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-pg10
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 73 sent by Profs. Hammersten and Caspersson, of the pancreas polynucleotide, which is said to resemble closely the nucleic acid from yeast: the comparison with the tniv nucleic acid preparation is shown in Pl. z, fig. q.. On the whole, considering these similarities, the repeated occurrence of a prominent refiexion at about 31 A., and the common high density, these experiments leave the reasonable impression that nucleic acids of the ribose type also are built up as columns of nucleotides, and that their main outlines of structure are similar to one another and to that of Na thymonucleate. «'e shall see below that this impression is very much strengthened, if not actually confirmed, by X-ray photographs of a recent, and highly poly- merized, preparation of the sodium salt of tnav nucleic acid; but before we go on to that it is worth while recording the results of a few more studies with the earlier preparations. One of these was of what may be called the `glassy' state that we observed on wetting the powder (as received) of yeast nucleic acid or pancreas polynucleotide with a little water on a microscope slide and allowing the gluey- mass to dry. Both preparations made in this way gave a diffraction pattern that is typical of the liquid or glassy state in that there is a clear space round the centre of the photograph (see Pl. z, fig. j). It is difficult at present to be sure of the correct interpretation of such photographs in the case of molecules of the complexity of the nucleic acids, but it is a plausible assumption that the position of the boundary of the clear space is a measure of the largest frequent distance of separation of molecules or aggregates. The clear space stops at about 16 A. in the pattern from the yeast glass, and at about iz A. in the pattern from the pancreas glass (incidentally, we failed to obtain the glass type of pattern with the virus acid); and the interesting point here is that this looks like another argument in favour of a piling of single nucleotides; in other words, it seems to be another argument against any idea that may still be current that a primary unit of the nucleic acids is a linked set of four nucleotides lying in a plane. Such a unit ,vould be some 4.o A. across, and we should expect the limit of the clear space to be appreciably nearer the centre of the photograph. Another interesting effect was observed when a mass of yeast nucleic acid powder was dropped into hot water. It developed a consistency something like that of chewing gum, so that it could be rolled out into strips. An X-ray photograph showed then the faint beginnings of orientation-in fact, this was our only, success of the kind with acids of the ribose type. Even so, the effect was too feeble to interpret, but it deserves further investigation. Attempts were also made to obtain fibre photographs of thymonucleic acid, specimens of which were prepared by Prof. Gulland and Dr Bailey. Dr Bailey's preparation was actually fibrous in appearance, but it turned out