46 PROTEINS. 



Four purine bases are obtained in which substitution occurs only in 

 pyrimidine ring ; these are 



Hypo-xanthine, .... 6-oxy-purine. 



Xanthine, ..... 2-6-dioxy-purine. 



Adenine, 6-amino-purine. 



Guanine, ..... 2-amino-6-oxypurine. 



Of, these, adenine and guanine have been isolated from milk, but the 

 presence of hypo-xanthine is doubtful. 



The nucleic acids are derivatives of purine bases, being compounds in 

 which a phosphoric acid radicle is condensed in the 8 position. 



Uric acid, which is excreted by the kidneys, has the composition of 

 8-oxy-xanthine. 



* M. Pyrimidine derivatives. 



Three pyrimidine derivatives are obtained from the nucleo-proteins : 



Uracil, .... 2-6-dioxy-pyrimidine. 

 Cytosin, .... 2-oxy-6-amino-pyrimidine. 

 Thymin, . .... 2-6-dioxy-5-methyl-pyrimidine. 



N. Glucosamine. 



H H OH H 



ill! 



CHo(OH) C C C C COH 



I I I I 

 OH OH H NH 2 



is obtained from the gluco-proteins. 



Glycine. Monoclinic crystals, soluble in 4-3 parts cold water. 

 Nearly insoluble in alcohol. M.P., 232 to 236 C., with dark 

 purple colour. Best obtained by the action of ammonia on 

 mono-chlor-acetic acid, or by the hydrolysis of glue. 



Alanine. Needles. Soluble in 4-6 parts cold water. Nearly 

 insoluble in alcohol. May be prepared from 2 parts aldehyde- 

 ammonia and 1 part hydrocyanic acid with excess of HC1. 



Leucine. Volatilises at 210 to 220 C. without melting, or 

 melts in a closed tube at 270 C. Moderately soluble in water, 

 and crystallises in soft nacreous scales consisting of concentrically 

 grouped rhombic prisms. 



Serine. Bunches of monoclinic crystals soluble in 32 parts 

 water at 10 and 24 at 20 C. Insoluble in alcohol. Active 

 form polarises -f 6, and the Isevo-form occurs in proteins. 



Aspartic acid. Prepared by the hydrolysis of asparagin, or 

 it may be separated from beet molasses. Polarises to the left 

 in water, and to the right in strong acids. Very soluble in hot 

 water, and little so in cold. 



Glutamic acid. Khombic-spheroidal-hemihedric crystals, melts 

 with decomposition at 202 to 202-5 C. One part soluble in 

 100 parts water at 16 C. ; less soluble in alcohol. May be pre- 

 pared by heating casein with HC1 and ZnCl 2 . 



* It is not certain whether pyrimidine derivatives occur in milk proteins. 



