The physico-chemical properties of ribonucleic acid of silkworms

There are few studies on animal ribonucleic acid (RNA) except those on the acid prepared from the spleen or liver of mamals. In a previous investigation, the author isolated desoxyribonucleic acid and RNA from silkworms (Bombyx mori) and, estimated their base compositions. In this paper, the method of preparation of the RNA was modified and its physico-chemical proporties as disclosed in the ultraviolet absorption spectrum, paper electrophoresis and ultracentrifugal sedimentation were investigated in comparison with yeast-RNA (Table 1). On the procedure of preparation of RNA from silkworms, the author, in the above mentioned previous study, used trichloroacetic acid to precipitate the cytoplasmic material from tissue-extracts with dilute aqueous cirtric acid solution. The usage of trichloroacetic acid is not very satisfactory both because it is expensive, and because there is danger that the RNA may be denatured by its strong acidity. The modification was, therefore, performed as follows: sodium chloride was added to the neutralized tissue-extracts until the solution reached O.14 M. Next, the solution was acidified to pH 4 with dilute hydrochloric acid. By these treatment the precipitation of cytoplasmic material was immediately produced. In order to isolate RNA from silkworms it is necessary to use tissue removed from their internal organs. When whole bodies including internal organs were used, fibrous material, which gave a nucleic acid-like absorption spectrum in the ultraviolet region but which contained small quantities of phosphorous and nitrogen, was obtained. This material contained a large quantity of pentose corresponding to 78 per cent of its contents in pure yeast-RNA. By paper chromatography of its hydrolysate no other sugar than ribose was detected. Its intrinsic viscosity and axial ratio were 1,300 and 150 respectively. In the ultracentrifugal analysis, a single homogenious component, the sedimentation constant of which was 5.8 S, was observed. In addition, paper electrophoretic and enzymatic experiments were undertaken. RNA on the paper electrophoregram was detected through the orange filter under ultraviolet ray after spraying it with an alcohol solution of eosine. The RNA of silkworms is distinguishable from that of yeast both in the composition of bases and in the depression of the absorption curve in the ultraviolet region (Fig. 1). The low absorption of silkworm-RNA may be due to the small quantity of adenine which it contains, for among the four bases in RNA, adenine shows the highest absorption at 260mμ. It is considered that the electric properties of nucleic acid may chiefly be due to phosphate radicals, and, hence, the small difference in composition of bases may have no effect on the properties. Actually, there are no differences between the electrophoretic mobility of these two RNAs. There is no distinction between the size of the molecules of each.家蚕から, 温和な方法で純粋にリボ核酸が取り出され, その理化学的性質が, 吸収スペクトル, 濾紙電気泳動及び超遠心沈降法によつて, 酵母リポ核酸と比較検討された. 両者は塩基組成に於て明らかに差異があり, 従つて光学的にも紫外部吸光の小なる事によつて区別される. 然し, その電気的性質には殆んど差別なく, 且つ, 分子の大きさにも顕著な差異は認められない