MOLECULAR CONFIGURATION IN SODIUM THYMONUCLEATE
MOLECULAR CONFIGURATION IN SODIUM THYMONUCLEATE
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DOI：
10.1038/171740a0
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发表时间：
1953-01-01
期刊：
影响因子：
64.8
通讯作者：
GOSLING, RG
中科院分区：
文献类型：
--
作者：
FRANKLIN, RE;GOSLING, RG
胸腺核钠纤维有两种不同类型的x射线图。第一种对应于晶体形式，结构a，在大约7.5%的相对湿度下获得；对此的研究在其他地方有详细的描述。在较高的湿度下，一种不同的结构，结构B，显示出较低的有序程度，在很大的环境湿度范围内出现并持续存在。从A到B的变化是可逆的。经历这种可逆变化的结构B纤维的含水量可能从干重的40% - 50%到数百%不等。此外，有些纤维从不显示结构A，在这些结构中，可以用更低的含水量获得结构B。结构B的x射线图（见图）以惊人的方式显示了螺旋结构的特征，螺旋结构最初是由斯托克斯（未发表）、克里克、科克兰和万德•在这个实验室里研究出来的。斯托克斯和威尔金斯首先通过对核酸纤维的直接研究提出了核酸的这种结构，尽管此前Furberg（论文，伦敦，1949年）在对核苷和核苷酸的x射线研究的基础上提出了螺旋结构。虽然x射线的证据目前还不能直接证明该结构是螺旋结构，但下面讨论的其他考虑因素使螺旋结构的存在极有可能。当胸腺核钠纤维吸收的水分超过其重量的40%时，结构B就产生于晶体结构A。这种变化伴随着纤维的长度增加了大约30%，并伴随着分子的大量重新排列。因此，似乎可以合理地假设，在结构B中，胸腺核钠的结构单元（分子群上的分子）相对不受邻近分子的影响
SODIUM thymonucleate fibres give two distinct types of X-ray diagram. The first corresponds to a crystalline form, structure A, obtained at about 7 5 per cent relative humidity; a study of this is described in detail elsewhere'. At higher humidities a different structure, structure B, showing a lower degree of order, appears and persists over a wide range of ambient humidity. The change from A to B is reversible. The water content of structure B fibres which undergo this reversible change may vary from 40--50 per cent to several hundred per cent of the dry weight. Moreover, some fibres never show structure A, and in these structure B can be obtained with an even lower water content. The X-ray diagram of structure B (see photograph) shows in striking manner the features characteristic of helical structures, first worked out in this laboratory by Stokes (unpublished) and by Crick, Cochran and Vand•. Stokes and Wilkins were the first to propose such structures for nucleic acid as a result of direct studies of nucleic acid fibres, alt, hough a helical structure had been previously suggested by Furberg (thesis, London, 1949) on the basis of X-ray studies of nucleosides and nucleotides. While the X-ray evidence cannot, at present, be taken as direct proof that the structure is helical, other considerations discussed below make the existence of a helical structure highly probable. Structure B is derived from the crystalline structure A when the sodium thymonucleate fibres take up quantities of water in excess of about 40 per cent of their weight. The change is accompanied by an increase of about 30 per cent in the length of tho fibre, and by a substantial re-arrangement of the molecule. It therefore seems reasonable to suppose that in structure B the structural units of sodium thymonucleate (molecules on groups of molecules) are relatively free from the influence of neighbouring