532 



CHEMISTRY OF THE PROTEIDS 



CHAP. 



and nitrogen- and the high oxygen-content, and this is owing to the 

 presence of the carbohydrate group which is rich in oxygen. The 

 high percentage of oxygen results, of course, in a low heat value. 1 

 Glyco-proteids contain also a relatively large amount of sulphur. 

 Little is known regarding their dissociation-products. Obolensky 2 

 obtained from an impure mucin, prepared from the submaxillary gland, 

 leucin and ty rosin ; Mitjukoff 3 from a pseudo- mucin, lysin and 

 arginin. On decomposing pseudo-mucin by means of strong mineral 

 acids Otori 4 found pseudo-mucin to cRffer from paramucin in only 

 giving rise to small amounts of humin substances, namely, 2 '6 2 65 

 grammes of humin from 43-369 dry, ash-free (calculated) pseudo-mucin ; 

 while Mitjukoff 3 obtained very large amounts from paramucin. Otori 

 gives the following table regarding the composition of pseudo-mucin : 



The amount of carbohydrate present varies greatly, being from 3 to 

 37 per cent. In the submaxillary mucin Miiller and Seemann 5 found 

 42 per cent glucosamin. 



All mucins give a violet biuret- reaction like the ordinary albumins, 

 and also the xantho-proteic and lead-sulphide reactions and the tests 

 of Millon and Molisch. The physical properties of the true mucins 

 are discussed below. 



The mucins and mucoids are not coagulated by heat, and differ in 

 this respect markedly from the native albumins and from most of the 

 proteids. They become, however, denaturalised when they are acted 

 upon by acids and especially by alkalies, or by alcohol and other 

 precipitating reagents, for they then no longer show their normal 

 mucilaginous character. This transformation or dissociation resembles 



1 P. B. Hawk and W. J. Gies, Amer. Journ. of Physiol. V. 387 (1901). 



2 Obolensky, Hoppe- Seyler s Med.-chem. Unters. p. 590 (1871). 



3 Kath. Mitjukoff, Dissertation, Bern, Arch. f. Oyndkol. 49 278 (1895). 



4 J. Otori, Zeitschr. f. physiol. Chem. 42- 453 (1904). 



5 F. Miiller and J. Seemann, Deutsche med. Wochenschr. 1899, \\ 209. 



