THE PROTEINS 



N.CH..CO 



C(OH)CH 2 .NH S 



(2) and (4) being the intramolecular form of the formulae (1) and (3). (3) and 

 (4) are sometimes spoken of as the enolic form. If we consider that perhaps 

 some hundred of the amino-acid groups may go to making up a single 

 protein molecule, it is possible to form some conception of the enormous 

 variability in reaction possible to such a compound. 



THE CONSTITUTION OF DIFFERENT PROTEINS 



All the proximate constituents of proteins, so far as we know, are amino- 

 acids. Of these the following have been isolated, namely, glycine, alanine, 

 amino-valerianic acid, leucine, isoleucine, proline, oxyproline, serine, phenyl 



alanine, glutamic acid, aspartic acid, tyrosine, tryptophane, cystine, lysine 

 histidine, arginine, and ' di-amino-trioxydodecoic ' acid. 



The question now arises whether all the different varieties of protein owe 

 their peculiarities to the presence of different amino-acids or whether the 

 greater number of the amino-acids above mentioned are present in all pro- 

 teins, the differences between the latter being determined by differences in the 

 arrangement and relative amounts of their proximate constituents. A large 

 number of analyses of different proteins have been made by Abderhalden, 

 Osborne, and others, utilising the methods for the isolation of amino-acids 

 devised by Fischer. The constitution of some representative proteins as 

 -determined in this way is given in the Table above. 



