超遠心機によるデオキシペントース核酸および核蛋白の研究
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Results of the ultracentrifugal studies on deoxypentosenucleic acid (DNA) and deoxypentosenucleoprotein (DNP) are presented in Parts 1 and 2, respectively. Part 1. Sedimentation coefficient and viscosity of five DNA preparations from herring sperm, and one each from calf thymus and sperm of rainbow trout were measured, and size and shape of DNA molecule were discussed. The value of s_0 (the sedimentation coefficient at infinte dilution) of the preparations obtained from fresh materials was 20〜25S (Svedberg units), which definitely exceeds the values hitherto reported for DNA (12〜15S). The molecular weight was estimated to be of the order of 5〜10 millions. The other preparations from not very fresh materials had lower s_0, and the lowest molecular weight was about 0.5million. Stability of DNA molecule through the course of purification was examined by comparing several samples at various stages of purification, including the original extract of DNP with strong saline. No marked irreversible change of size and shape of DNA was observed. The shape of DNA molecule in solution was discussed by considering the relationship between s_0 and [η] (limiting viscosity number) of the various preparations. A coil model, fairly "stiff" as compared with typical random coil, is compatible with the experimental results, but rigid, prolate ellipsoids of revolution with a constant minor axis is not. Observation of the shape of the sedimentation boundary of these preparations led to the view that the DNA preparations are considerably heterogeneous with respect to molecular weight. This is consistent with the observation that mixtures of two preparations with widely different molecular weights showed only a single, normal sedimenting boundary. Part 2. Interaction between DNA and basic protein in strong saline at neutral pH was studied in cases of nucleohistone from calf thymus (TNH), nucleoprotamine from sperm of rainbow trout and artificial mixture of purified preparations of DNA and histone. Sedimentation coefficient and viscosity of calf thymus nucleohistone in strong "saline were found to depend strongly upon sodium chloride concentration. The results, together with the high speed centrifugation experiment, indicated that in 1M sodium chloride solution a considerable amount of histone is bound to DNA to form complex molecule with smaller hydrodynamic resistance than free DNA and the complex dissociates progressively with increase of sodium chloride concentration. It is histone I (the arginine-rich component) and not histone II (the lysine-rich component) that is bound to DNA. Concordant results were obtained with artificial mixtures of DNA and calf thymus histone. Histone I chloride formed complex molecule with DNA in 1M sodium chloride solution similar to the one found in natural TNH. Fish sperm DNA interacted with histone I chloride as strongly as calf thymus DNA. However, aggregation of histone I chloride disturbed the interaction with DNA; histone II chloride and histone sulfates (I and II) showed practically no interaction with DNA in solution. In sharp contrast to TNH, nucleoprotamine seemed to be fully dissociated into DNA and protamine throughout the range of sodium chloride concentration studied (0.83〜2.9M). Thus the interaction between DNA and basic protein in strong saline solution depends strongly upon the nature of the protein, although these mixtures gave typical precipitate of "DNP" when diluted to 0.14M sodium chloride.
- 宇宙航空研究開発機構の論文
- 1957-02-25
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