ENZYMES — KILBY 



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THEORIES OF ENZYME ACTION 



In short, life as we know it could not exist without enzymes. 



Various theories have been proposed to try and explain how en- 

 zymes can so modify chemical reactions that they will occur under 

 such mild conditions. The general idea of the most widely held 

 theory is as follows: Suppose a molecule, say A-B, is too firmly 

 bound together for breakage of the bond between A and B to occur 

 easily, then if complex formation takes place with an enzyme, the 

 forces holding the complex together may lead to a redistribution 

 of forces within A-B such that the linkage is so weakened that 

 fission can occur and A and B are formed. This idea is shown pic- 

 torially in figure 3, but it must not be taken too literally. 



The substrate molecule approaches the active center 

 on the enzyme surface. 



An enzyme-substrate complex is formed, if'the shapes 

 and reactivities of the two parts are favorable. 



The binding forces lead to the weakening of a chem- 

 ical bond in the substrate molecule. 



Fission occurs, and the two fragments leave the ac- 

 tive center which is free for another cycle to occur. 

 The fragments may be highly reactive, and may com- 

 bine with other substances. 



Figure 3. 



