302 PRACTICAL ORGANIC AND BIO-CHEMISTRY " 



Preparation of Plant Nucleic Acids. 



These nucleic acids are most simply prepared by the method of Clarke 

 and Schryver. 1 The material is boiled with alcohol to render the proteins 

 insoluble and extracted with i o per cent, sodium chloride solution ; on acidify- 

 ing the extract, the nucleic acid is precipitated. In the case of wheat embryos 

 it is advantageous to digest away the starch previous to the extraction. 



(i) Preparation 0} Yeast Nucleic Acid. 



30 Ibs. of freshly pressed yeast are mixed with excess of 95 per cent, 

 alcohol and allowed to stand for 24 hours. The alcohol is filtered off on a. 

 Buchner funnel and the solid dried in the air. 



The air-dried solid, in portions of i kilo., is boiled for 2 hours with 95 

 per cent, alcohol, filtered off, pressed, dried in an air current at 37 and ground 

 to a fine powder, i kilo, of this material is extracted for 4-5 days with 10 

 litres of 10 per cent, sodium chloride solution at 60-80, the mass being raised 

 to this temperature daily and allowed to cool slowly. The extract is strained 

 through muslin and the residue pressed out. The extract is filtered clear 

 through paper and acidified with dilute hydrochloric acid (i : i) which is added 

 with vigorous stirring. Nucleic acid separates and settles out as a hard cake. 

 After 2 hours the liquid is syphoned off; the crude nucleic acid is washed 

 with 50 per cent, alcohol till free from chlorine, left under 95 per cent, alcohol 

 for 24 hours, washed with absolute alcohol and ether. A fine light brown 

 powder in a yield of i -5 per cent, is obtained. The crude nucleic acid (20 gm.) 

 is purified by dissolving in 10 per cent, sodium acetate solution (500 c.c.), 

 filtering from insoluble matter, adding ico c.c. of alcohol and acidifying with 

 hydrochloric acid. A white mass separates ; it is washed with 50 per cent, 

 alcohol, 95 per cent, alcohol, ether and dried in vacua. This preparation 

 contains 9-3 per cent, of phosphorus and 16*4 per cent, of nitrogen. Further 

 purification is effected by dissolving 5 gm. in 200 c.c. of water and 100 c.c. of 

 o-i per cent, caustic potash and precipitating the clear solution with 20 c.c. 

 of '5N hydrochloric acid. An equal volume of alcohol is added, the pre- 

 cipitate of nucleic acid is filtered off, washed with alcohol and ether and dried 

 in vacua. It contains 9-6 per cent, of phosphorus and 16*4 per cent, of 

 nitrogen. 



(ii) Preparation of Wheat Nucleic Acid (Triti co-nucleic acid). 



i kilo, of fresh wheat embryos is boiled for 2 hours with 3 litres of 95 per 

 cent, alcohol, filtered and pressed free from the liquid and dried in the air. 

 The air-dried material is put in small portions at a time in 10 litres of water 

 and heated for 2 hours in a boiling water- bath to gelatinise the starch. The 

 thick paste so formed is transferred to two flasks and cooled to 40 and to each- 

 are added 2*5 gm. of takadiastose. The liquids are covered with a layer of 

 toluene and fermentation allowed to continue till starch can no longer be de- 

 tected. The liquid is boiled, cooled, sodium chloride added so as to make a 

 10 per cent, solution of salt, and heated daily for 4-5 days to 60-80. The 

 solution is filtered through paper pulp and pressed out from the residue. 100 

 c.c, of hydrochloric acid (i : i) are added to the clear filtrate. The precipitate 

 of crude nucleic acid is washed free from chlorine with 50 per cent, alcohol, 

 left under 95 per cent, alcohol, washed with absolute alcohol and ether and 

 dried in vacua. Yield = 7 gm. 



Purification of the nucleic acid is carried out by solution in 400 c.c. of 

 0*1 per cent, caustic potash, precipitation with hydrochloric acid, washing 

 with alcohol and ether and drying in the air. This product contains 8*9 per 

 cent, of phosphorus and 16*3 per cent, of nitrogen. 



1 Biochem. J., 1917, II. 



