466 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



presence of phosphorus in a protein precipitate whether organic or 

 inorganic has sufficed to place it in the class of nucleoproteins. The 

 only characteristic of a nucleoprotein is the presence of nucleic acid 

 and the formation of purine and pyrimidine bases on hydrolysis. 

 Nucleoproteins may be distinguished from phosphoproteins by the 

 action of alkali ; the former are stable and do not yield phosphoric 

 acid on hydrolysis by alkali. 



Nucleoproteins of the Thymus. 



The thymus contains two nucleoproteins a nucleo-historie and a 

 nucleoprotein. 



Thymus /3-Nucleohistone. 



Preparation (Bang). 



The minced thymus is treated for i or 2 days with water containing 

 toluene. The fluid is separated by straining and centrifugalisation. Calcium 

 chloride is added to it until it contains -2 per cent. The precipitate is 

 separated by centrifugalisation. The filtrate contains nucleoprotein (below). 

 It is stirred up with (i) alcohol which is decanted and (2) water. After 

 several hours the precipitate is filtered off and stirred up with 2 per cent, 

 sodium chloride solution. After 24 hours the liquid is filtered off. It is clear, 

 has a bluish fluorescence and is diluted so that it contains i per cent, of 

 sodium chloride. The precipitate of nucleohistone is filtered off, dissolved in 

 water and thrown down by adding calcium chloride until '2 per cent, is present. 

 Solution in water and precipitation with -2 per cent, calcium chloride is re- 

 peated several times. 



Properties. 



Thymus nucleohistone is insoluble in water, but its ammonium and alkali 

 salts are easily soluble in alkali and ammonia. Sodium chloride precipitates 

 sodium histone nucleate, which is soluble in 2 per cent, sodium chloride 

 solution. Histone is precipitated if more salt be added. 



It behaves in a similar way towards magnesium and ammonium sulphate ; 

 a precipitate is formed, soluble in excess ; it is not precipitated by saturation 

 with magnesium sulphate, but it comes down with 70 per cent, of ammonium 

 sulphate. 



It is decomposed by alkalies and ammonia ; by the action of ammonia 

 histone is formed ; it is also decomposed by "3 per cent, of hydrochloric acid, 

 but by weaker acids nucleohistone is precipitated from solution. 



Thymus a-Nucleoprotein. 



Preparation. 



A precipitate of thymus nucleoproteins is formed on adding dilute acetic 

 acid to the filtrate from the calcium chloride precipitate (above). It is 

 easily soluble in excess of acid, particularly hydrochloric acid. 



Thymus nucleoprotein is obtained by extracting thymus glands with 0*9 

 per cent, sodium chloride solution. The nucleohistone does not dissolve. 

 The extract is acidified with acetic acid. 



Properties. 



The a-nucleoprotein of the thymus is not precipitated by salt and very 

 incompletely by calcium chloride. It is precipitated by saturating its solution 

 with sodium chloride or magnesium sulphate and by 25-30 per cent, saturation 

 with ammonium sulphate. It is thus more easily precipitated than the 

 nucleohistone. 



It is decomposed by dilute hydrochloric acid into protein and nucleic 

 acid ; the protein is of the nature of acid metaprotein. 



