ENZYMES 



lysts known as enzymes. Apparently, there is a different enzyme for 

 practically every reaction, or at least every reaction type of intermediary 

 metabolism. This can only mean that some several thousand en- 

 zymes must exist. For a long time fears were expressed that the 

 cramped quarters of the average small sized cell could not possibly 

 accommodate so many different enzymes. But that bogey has been 

 laid low by the isolation from one small cell such as the yeast cell of 

 literally hundreds of different enzymes. Of course, not all types of 

 cells have the same complement of enzymes. The number and amount 

 of enzymes vary from one cell type to another, and in fact determine 

 the individuality of each cell. 



There are many instantaneous ionic reactions which occur in 

 the course of intermediary metabolism and which do not require 

 enzymes, e. g., neutralization of acids or bases, and deposition of salts 

 such as calcium phosphate. But even in the province of reactions 

 which occur spontaneously, a surprise is occasionally in store. Thus, 

 the decomposition of carbonic acid into carbon dioxide and water is 

 catalyzed by a special enzyme known as carbonic anhydrase, which can 

 speed up the rate of the reaction far beyond the spontaneous rate. 



The study of intermediary metabolism represents one of the 

 oldest lines of biochemical investigation. It is not surprising, there- 

 fore, that of the total number of reactions known to occur in inter- 

 mediary metabolism only a very small proportion have been recon- 

 structed with isolated enzyme systems. In fact, whole chapters of 

 intermediary metabolism such as the metabolism of steroids, porphyrins, 

 carotenoids, sulfur compounds, bile acids, fatty acids, etc., are prac- 

 tically virgin territory as far as knowledge of enzymes is concerned. 

 Enzyme chemistry has made its greatest strides in the field of fermenta- 

 tion or glycolysis of sugar. Here, the entire process from glucose to 

 glycogen or from glycogen to lactic acid has been reconstructed in 

 vitro with some twenty odd enzymes, each prepared in pure or largely 

 pure state. This in vitro reconstruction is not to be regarded as a 

 stunt or merely as a triumph of biological engineering. In order to 

 effect a successful reconstruction, it becomes necessary to understand 

 precisely the way in which certain enzyme systems are linked together 

 and the way in which different chemical reactions are synchronized. 

 A successful reconstruction, therefore, implies mastery of most of the 

 chemical details and a complete knowledge of the constituent enzyme 



