THE PROTEINS 



8l 



group, so that the still more complex peptids can be formed. When this is 

 done there is yet a carboxyl and an amino group to which other amino acids 

 can similarly be joined. The structure of the protein molecule accordingly 

 may be represented as follows: 



H 



H 



H 



- OC - C - NH - OC - C - NH - OC - C - NH - 



R 



R 



R 



In which R indicates here the rest of the formula for any of the a-amino 

 acids entering into the constitution of protein. 



At least eighteen amino acids have been found to enter into the composi- 

 tion of the proteins. The list includes glycocoll, alanine, serine, phenyl- 

 alanine, tyrosine, tryptophane, cystine, leucine, isoleucine, amino-butyric 

 acid, aspartic acid, glutaminic acid, proline, oxyproline, histidine, arge- 

 nine, lysine, and diaminotrihydroxydodecanoic acid. Associated with 

 the amino acids there is usually a detectable amount of amino-carbohydrate. 

 The chemical formulae for the more important of these are given below: 



NH 2 



H-C-COOH 

 H 



Glycocoll. 



H NH 2 



I I 

 H -C-C-COOH 



H H 



Alanine. 



H NH 2 



I I 

 C - C-C-COOH 



/S I i 



HC CH H H 



I I 

 HC CH 



C 

 H 



Phenylalanine. 



(amino acetic acid.) (a-amino proprionic acid.) (Phenyl a-amino proprionic acid.) 



H NH, 



H H 



OHNH 2 



H-C-C-COOH 

 H H 



Serine. 



(a-amino /3-hydroxy 

 proprionic acid.) 

 6 



I I 

 C - C-C-COOH 



HC CH H H H-C-S-S-C-H 



HC CH 

 C 



Tyrosine. 



(p-oxyphenyl a-amino 

 proprionic acid.) 



| I 



H-C-NH 2 H-C-NH 2 



I I 



COOH COOH 



Cystine. 



