CHAPTER VIII. 

 COMPOUNDS OF THE PROTEINS. 



TYPES OF UNION IN THE PROTEIN MOLECULE. 



Following the recognition of the fact that the proteins are complexes 

 built up by the union of amino-acids, the question of the mode of union 

 between them became one of paramount importance. Hofmeister 

 has pointed out that it is possible to conceive of several ways in 

 which amino-acids might be linked together, such as : 

 A. Direct union of the carbon atoms, as: 



under which condition the molecule would be an immense chain of 

 carbon atoms and if the addition of the elements of water (hydrolysis) 

 were to accomplish the splitting up of the molecule, a large proportion 

 of hydroxy-acids would result: 



+ H.OH = CH + HOC 



I I 



whereas hydroxy-acids (tyrosine, serine and oxyproline) form, as a 

 rule, only a small proportion of the products of protein hydrolysis. 

 Direct union of carbon atoms, therefore, cannot be a frequent mode of 

 linkage of amino-acids within the protein molecule. 



B. Ether-like unions, as: 



I I 



I | 



Such unions, however, would only be possible when one of the two 

 amino-acids thus united contained a hydroxyl-group and, as we have 

 seen, hydroxy-amino-acids constitute only a small proportion of the 

 total amino-acids yielded by a protein when it is hydrolyzed. 



C. The carbon atoms may be united through a nitrogen atom as: 



I I I 



C N C 



I I 



Several varieties of this mode of union are possible, as: 



CH* NH CH2 CH* NH CO 



I. II. 



CH2 N(OH) = C CH2 NH C(NH) 



III. IV. 



