34 THE GENERAL CHARACTERS OF THE PROTEINS 



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product is in almost all instances obtainable, viz^ ammonia. The 

 relative amount of these bodies forms a factor which is characteristic 

 of each individual protein. As to the origin of the ammonia but 

 little is known. It is possibly derivable from asparagine or some 

 allied amide which pre-exists in a conjugated form in the protein 

 molecule. The nitrogen obtainable in the form of ammonia by the 

 hydrolysis of proteins is consequently designated " amide-nitrogen ". 

 The nitrogen of the monoamino-acids is known as " monoamino- 

 nitrogen," that from the diamino acids, which can be distinguished 

 from the monoamino-acids by the fact that the former only are 

 precipitable by phosphotungstic acid, as "diamino or basic nitrogen". 

 In addition to the nitrogen in the above forms a small quantity of 

 pigmented bodies are formed during hydrolysis ; the nitrogen con- 

 tained in these bodies is generally designated as " humin " nitrogen. 



Systematic experiments on the determination of the distribution 

 of nitrogen amongst the various forms of hydrolysis products were 

 carried out by Hausmann in Hofmeister's laboratory, and the per- 

 centages in the various forms of amide, monoamino, diamino and 

 humin nitrogen are often referred to as the " Hausmann numbers ". 



In the method originally devised by Hausmann the following 

 operations were carried out : (i) the hydrolysis of the proteins with 

 hydrochloric acid ; (ii) the determination of the amide-nitrogen by 

 distillation of the diluted hydrolysis products with magnesium oxide, 

 by means of which the ammonium salts are decomposed, and the 

 estimation of the ammonia evolved by collecting it in a known 

 amount of standard acid ; (iii) the precipitation, after distilling off 

 the ammonia, of the residual liquid with phosphotungstic acid, where- 

 by the diamino-acids are precipitated, and the determination of the 

 nitrogen in this precipitate ; (iv) the estimation of the nitrogen in 

 the filtrate from the phosphotungstic acid precipitate. This gives 

 the nitrogen of the monoamino-acids (also estimated by the subtrac- 

 tion of the other numbers from the total). 



Several objections were raised to the method of Hausmann 

 shortly after it was published, notably by Henderson, Kutscher, and 

 by Schulze and Winterstein. It was urged against it by Hender- 

 son that the amounts of " amide-nitrogen " varied when different 

 strengths of acid and varying times of hydrolysis were employed. 

 Kutscher objected to the method on the ground that the diamino-acids 

 were not entirely insoluble in water and excess of phosphotungstic acid. 

 Schulze and Winterstein, furthermore, claimed that certain monoamino- 

 acids such as phenylalanine were precipitable by phosphotungstic 

 acid. Another objection raised was that by treatment with magnesia 

 ammonia was evolved from substances other than ammonium salts. 



These objections have been subjected to a critical examination by 

 T. B. Osborne and Harris, and by Gumbel. The former investi- 

 gators have shown that identical numbers can be obtained where 

 the conditions of experiment vary even within fairly wide limits, 

 although they admit with Henderson that different u amide-nitrogen " 

 numbers, for example, can be obtained by acids of different concen- 

 trations and by varying periods of hydrolysis. They show, how- 

 ever, that variations in conditions necessary to produce different 

 results must be large, and that, provided that certain readily specified 

 conditions be adhered to, valuable comparative results can be ob- 



