Complex Compounds and Models of Enzymes 269 



the compound of catalase with hydrogen peroxide must be attributed to the whole 

 complex and not to individual functional groups, for the spectra of these com- 

 pounds differ from the spectrum of the enzyme owing to displacement of the 

 energetic level brought about by complex-formation [7]. 



The structure formed by the addenda surrounding the central ion must 

 obviously, in itself, play an important part in determining the catalytic functions 

 of the compound. This is to be seen from the fact that complexes of amines with 

 other metals (zinc, cadmium, silver and cobalt), though their catalase-like 

 activity is far less than that of copper compounds, are subject to the general 

 rules relating structure to activity. So far as one can judge from the limited data 

 available, the sequence of arrangement of addenda which is responsible for an 

 increase in activity in copper compounds is essentially the same for the other 

 metals mentioned above. 



Let us now turn to the oxidase-like activity of complexes. I intend to limit 

 myself to a consideration of complexes which do not themselves contain a mole- 

 cule of the substrate to be oxidized and which, therefore, do not lose the typical 

 peculiarities of their structures in the course of the reaction. Porphyrins are 

 complexes of such a type; however, they cannot be regarded simply as models, 

 since they are, themselves, the active groups of enzymes. 



We have succeeded in increasing the oxidase-like activity of the copper ion in 

 respect of the oxidation of pyrogallol by oxygen, by the direct combination of 

 the copper ion with ethanolamines, diamines and heterocyclic compounds of the 

 pyridine series [10]. These compounds are probably among the simplest models 

 of the active group of polyphenol oxidase. The reaction of oxidation of ascorbic 

 acid is catalysed by complex compounds of the iron ion with pyrocatechin and 

 antipyrin. 



It is of the utmost interest that the addenda themselves, i.e. various amines, 

 are good catalysts in the oxidation of pyrogallol [18]. However, when they are 

 combined with a copper ion the activity is increased considerably so that the 

 activity of the complex is far greater than the sum of the activities of the ion 

 and the addendum. 



In order to decide to what extent the complex compounds discussed above 

 merit the name of models of active groups we must make a thorough analysis of 

 the mechanism of their action and of the thermodynamic pecuHarities charac- 

 teristic of catalysis of this sort. As concerns the reaction mechanism, we must 

 choose between an explanation based on the radical-chain theory and a treatment 

 according to the theory of intermediate products. The rapid progress made by 

 the radical-chain theory justifies the attempt to apply the same concepts to the 

 mechanism of the action of enzymes [11]. 



However, it has now become clear, especially since the work of Chance, that 

 an important part in the mechanism of action of many enzymes, catalase in 

 particular, is played by an intermediate, enzyme-substrate product.* It is well 

 known that the kinetic side of the theory of intermediate products was worked 

 out in detail long ago (e.g. in the works of Michaelis) and agrees well with 



* A. Goudot [17] believes that the ion of the metal may combine with electrons of the 

 hydrogen peroxide molecule. 



