ANTIGENS AS BIOCATALYSTS 11 



of the known type reactions. All chemical reactions take place ac- 

 cording to a stoichiometrical relationship; that is, there exist numer- 

 ical relations between elements or compounds in combining to form 

 a new compound, or in tautomerizing to a new isomer, or in dissociat- 

 ing into elements or compounds. They do so according to definite 

 proportions by volume and weight. Various influences, such as heat, 

 light, or catalysts do not affect this relationship. 



The influence of a catalyst does not change the stoichiometrical 

 relationships. The catalyst does not alter the free energy of the reaction; 

 it does not enter into any irreversibly stable union with either the 

 reactants or the reaction products. It simply speeds up the reaction to 

 attain the equilibrium in a shorter period of time. In many cases the 

 reactions, in the absence of a catalyst, proceed at such a slow rate that 

 one cannot detect their presence, but vdth the introduction of a 

 suitable catalyst the reaction becomes obvious. 



The structures of organic substances express mechanical and chemi- 

 cal meaning. All atoms or groups of atoms at special positions in the 

 space occupied by the structure of a molecule determine the chemical 

 and physical behavior of the whole molecule, and its groups as well. 

 Any change in the spatial relationships of the functional groups as a 

 whole causes a corresponding change in properties. A given empirical 

 formula of an organic compound will often represent several isomeric 

 compounds of the same molecular weight and elementary analysis, 

 such as, for example, the cis and trans isomers, fumaric and maleic 

 nature. 



HOOC— C— H H— C— COOH 



II II 



H—C— COOH H— C— COOH 



Fumaric acid Maleic acid 



which have different physical and chemical properties. There are large 

 numbers of isomers which may differ from each other only by a single 

 physical property, namely, by the ability to rotate the plane of polarized 

 light in a different direction, d- and 1-fructose, d- and 1-lactic acid, 

 d- and 1-alanine, etc., represent the class of a large number of optically 

 active isomers. What interests us here is that some of these isomers are 

 interconvertible under the influence of accelerating agents of catalytic 

 nature. 



In general, chemical reactions take place either (a) by the applica- 



