78 IMMUNO-CATALYSIS 



knowledge as to the finer structure of proteins to formulate a com- 

 prehensive mechanism of antibody formation for correlating its 

 chemical and physical properties with that of the specificity of sero- 

 logical reactions. In this connection it might not be irrelevant to re- 

 view some of the properties of proteins pertinent to our question. 



1. An Introductory Comment on the Antigenic 

 Specificity of Proteins 



We know that the proteins differ in a general way in their physico- 

 chemical properties— solubility, iso-electric point, electric charge, 

 molecular weight and shape, etc. We do not know very much about the 

 spatial configuration, but we know that one protein might diflfer from 

 others in the arrangement and content of amino acids. A protein might 

 be simple or conjugated with nucleic acid, heme, coenzyme, carbohy- 

 drate, lipoid, etc., but none of this information has as yet clarified 

 the subject. It has further been known that all proteins are con- 

 structed of a large number of a-amino acids which are combined 

 through peptide bonds, thus forming a long chain containing many 

 CO-NH groups or peptide bonds. The proteins contain (in the ab- 

 sence of c-amino acid) practically no free amino or a-carboxyl groups. 

 Consisting solely of 1-amino acids with the exception of glycine, which 

 has no asymmetric carbon atom and thus no optical activity, the 

 proteins have uniform optical configuration. Specificity of proteases 

 is singularly limited to the hydrolysis or synthesis of molecules of 

 1-configuration. These enzymes have no effect on the d-amino acids. 

 For example, glycine (glycocoll or a-amino-acetic acid, NH2CH2- 

 COOH) and alanine (a-amino-propionic acid, CH3CHNH0COOH) 

 can form four different dipeptides: (1) glycylglycine, (2) alanyla- 

 lanine, (3) glycylalanine, (4) alanylglycine. It is significant that 

 peptides 3 and 4, although giving the same amino acids on hydrolysis, 

 are not the same. This gives some clue to the possibilities of com- 

 binations of the amino acids in proteins. It can be seen that when the 

 number of amino acids available for such head-tail amide formation 

 is increased, the number of combinations due to the order in which 

 they are linked increases very rapidly. Emil Fischer (1923) starting 

 with glycylglycine synthesized an octadecapeptide with a molecular 

 weight of 1213. He calculated that out of 30 amino acids, 18 of which 



