THE NITROGENOUS SUBSTANCES 71 



centage of monamino acids in the proteid molecule is by no means small: 60.2 

 per cent of the total nitrogen in crystallized serum albumin, 67.8 per cent in 

 crystallized egg albumin, 55.0 per cent in crystallized edestin, 68.3 per cent in 

 serum globulin (horse). 



7. Carbohydrate groups. In many proteids, but not in all, there is a nucleus 

 which on total cleavage appears regularly as glucosamin (CH 2 (OH) .CH(OH). 

 CH(OH).CH(OH).CH(NH 2 ).CH:O) (F. Miiller). Besides this nucleus, or 

 in its place, nitrogenous or nonnitrogenous carbohydrate complexes may also be 

 present. 



Among the simple native proteids there appears to be only one thus far 

 known, namely, edestin, which contains no carbohydrate group in its molecule. 

 In the others the number of these groups varies considerably. Crystallized egg 

 albumin contains at least 10.0 to 11.0 per cent of glucosamin, submaxillary mu- 

 cin 20.8 per cent of reducing substance, pseudomucin from ovarial cysts 30.0 

 per cent, egg mucoid 34.9 per cent, and the mucin of sputum 36.9 per cent. In 

 crystallized serum albumin the content is very small. 



8. A monamino acid of the benzol series, namely, the para-phenyl-amino- 

 propionic acid (phenylalanin,/^CH 2 .CH(NH 2 ) .COOH) and 



\/ 



9. The corresponding para-oxy-compound, p-oxy-phenyl-amino-propionic acid 

 (tyrosin, CH 2 .CH(NH 2 ) .COOH) 



In most proteids tyrosin occurs in far greater quantity than phenylalanin. 

 The maximal yield of tyrosin is 1.5 per cent in crystallized egg albumin, 2.0 

 per cent in serum albumin, 3.0 per cent in fibrin, 6.3 per cent in thymus histon 

 and 10.1 per cent in zei'n. 



10. From numerous observations on the cleavage products formed in putre- 

 faction of proteid, it appears that an indol nucleus is present. It is likely that 

 this nucleus in very small quantities is changed into /3-methyl-indol-amino-acetic 

 acid (tryptophan, 



OH 



CH C C.CH 3 



OH C.CH.(NH a ).COOH 



\ /\ / 

 CH NH 



Hopkins and Cole). 



11. The heterocyclic pyrrolidin nucleus is represented among the cleavage 

 products of different proteids (edestin, serum albumin, serum globulin, egg albu- 

 min, fibrin) by the a-pyrrolidin-carboxylic acid 



CH a -CH, 



CH, CH.COOH 



and 



12. By the oxy-a-pyrrolidin-carboxylic acid 



CH, CH.OH 

 CH, CH.COOH 

 NH 



(Fischer). 



