20 CHEMICAL STATICS 



of the free amino nitrogen determinable in the native proteins 

 by the nitrous acid method. The a-amino groups which con- 

 stitute the remaining and greater part of the free amino nitrogen 

 found after complete hydrolysis are, in the intact protein mole- 

 cule, practically all condensed into peptid linkings. 



In the primary albumoses or first split-products of protein 

 hydrolysis, the relations are different. The free amino groups 

 in hetero- and protoalbumose exceed one-half the content of 

 lysin nitrogen by 3.0 and 4.8 per cent of the total nitrogen re- 

 spectively, indicating that an appreciable proportion of the 

 a-amino groups are uncovered in even the first steps of hydrolysis. 



8. Some Consequences of the Polypeptid Structure of the 

 Protein Molecule. — The polypeptids are as essentially amino- 

 acids as the amino-acids out of which they are built up. Thus 

 glycyl-glycin is as typically an amino-acid as glycocoll itself, 

 since it possesses an — NH2 group as well as a — COOH group 

 and for this reason is presumably capable of forming compounds, 

 not only with acids and bases, but also with neutral salts (52). 

 On undergoing electrolytic dissociation it may be supposed to 

 jdeld either hydrogen (H+) ions, or hydroxyl (OH') ions, owing 

 to the occurrence of a reaction with water of the type: 



/NH2 /NH3OH 



R^ -t-H.OH = Rf 



^COOH ^COOH 



just as ammonia, in aqueous solution, partially reacts with water 

 toformNH40H. 



It is usually conceded that these elements in the structure of 

 the proteins afford an explanation of the power which they pos- 

 sess of neutralizing both acids and bases, in other words the 

 "amphoteric" character of the proteins. To this opinion I have 

 also formerly inclined, but an accumulation of data irreconcil- 

 able with this view induced me some years ago (57) to abandon 

 it. Since that time evidence of a perfectly conclusive character 

 has been obtained and we may now regard it as an established 

 fact that some elements in the protein molecule other than ter- 

 minal — NH2 or — COOH groups are responsible for the acid- and 

 base-neutralizing power which is possessed in such a marked 

 degree by many proteins (vide Chapters IV and V). 



In the first place, the investigations of Levites and D. D. Van 

 Slyke, referred to above, have shown that only a very small 



