NUCLEIC ACIDS 301 



liquid be acidified with acetic acid a precipitate is formed. This 

 precipitate on purification does not contain protein. It is a mono- 

 nucleotide, termed guanylic acid, and consists of guanine, pentose 

 and phosphoric acid. Another mononucleotide, inosinic acid, has 

 been prepared from meat extract. It consists of xanthine, pentose 

 and phosphoric acid, and is identical with vernine, a mononucleotide 

 prepared from plants. 



These y8-nucleoproteins of animals have thus the constitution of 

 plant nucleic acids. They are not constituents of the nuclei of 

 animal cells, but have been ingested by the tissue from vegetable food. 



The work of the various investigators upon nucleic acid is given 

 by Walter Jones in his monograph on Nucleic Acid. 



Preparation of Nucleic Acid from Thymus, etc. 



There are various methods for preparing nucleic acid, but the following 

 given by W. Jones is most convenient : 



i kilo, of thymus, freed from fat, connective tissue, etc., and finely minced, 

 is added in small portions to 2 litres of boiling water containing 33 gm. of 

 sodium hydroxide and 100 gm. of sodium acetate. The material dissolves 

 giving a pale brown solution : lumps are removed and brought into solution 

 separately by heating over a flame. The solution is heated in a boiling water- 

 bath for 2 hours with occasional stirring. It is diluted with one-third of 

 its volume of water and acidified to litmus with 50 per cent, acetic acid; 

 about 100 c.c. are required. The proper acidity must be obtained so as to 

 ensure rapid filtration ; it can be attained by adding acetic acid or sodium 

 hydroxide as may be required. The solution is heated to boiling and filtered 

 through a hot-water funnel. It will gelatinise on cooling. The solution 

 and washings are evaporated to 750 c.c. and poured slowly into i litre of 95 

 per cent, alcohol. Sodium nucleate mixed with phosphates is precipitated. 

 After 1 2- 1 6 hours the liquid is decanted away and the precipitate pressed 

 out, washed with 80 per cent, alcohol and 90 per cent, alcohol, the final parts 

 of the washings being pressed out. The precipitate is placed in a flask with 300 

 c.c. of water and heated on a water-bath. The phosphates collect leaving a 

 clear liquid. To facilitate filtration through a hot-water funnel 10 c.c. of 20 

 per cent, sodium hydroxide are added. The filtrate is acidified with acetic 

 acid and poured into 75 c.c. of 95 per cent, alcohol. The liquid is decanted 

 and the precipitate washed as before. It is ground up in a mortar with one 

 or two changes of absolute alcohol a greater amount of washing causes 

 ^mulsification and it crumbles to a fine powder, which is filtered off and 

 washed with alcohol and dried in a desiccator. About 33 gm. of sodium 

 nucleate are obtained from i kilo, of thymus. 



Nucleic acid can be obtained by pouring the solution into about 3 volumes 

 of alcohol containing 2 c.c. of concentrated hydrochloric acid per 100 c.c. 



Properties. 



Nucleic acid is a white powder, insoluble in alcohol and ether, but soluble 

 in alkalies and ammonia ; it is insoluble in water forming a slimy mass. It is 

 not precipitated from dilute alkaline aqueous solution by acetic acid, but it is 

 -precipitated by mineral acids. Acetic acid will precipitate nucleic acid from 

 concentrated solutions in the presence of small amounts of alkaline acetates. 



The sodium salt dissolves in water ; a 4 per cent, solution gelatinises. The 

 solutions are optically active. The phosphorus and nitrogen content serve to 

 characterise nucleic acid, but proper characterisation is only possible by an 

 analysis of its decomposition products. 



