ORIGIN OF ENZYMES 373 



We have pointed out above that the very highly developed 

 structures of catalase, carboxylase or any other enzyme could 

 not have arisen by the action of selection on their separate 

 isolated molecules, because the reactions which they carry 

 out are of no significance to the catalase or carboxylase them- 

 selves. Their hastening or slowing of reactions cannot be 

 reflected in the length of the existence or an increase in the 

 amount of the enzymes as such. This activity may, however, 

 have a decisive effect on the existence of the system in which 

 any particular catalyst acts. Thus these systems must have 

 been selected for the characteristic in question, and thus 

 there could have arisen that extreme ' purposefulness ' of 

 structure, that correspondence between structure and func- 

 tion, by which enzymes may be recognised as biological 

 formations. 



Indeed, although we are now very rapidly approaching a 

 full understanding of the chemical nature of enzymes, and 

 even the solution of the problem of their synthesis by arti- 

 ficial means, these catalysts still bear all the marks of their 

 biological origin. In nature they are only to be found in 

 organisms and can only be formed naturally there. Such a 

 ' fortunate ' combination of atomic groups as we find in 

 enzymes, such an intimate association between their struc- 

 tures and their biological functions, could not have arisen 

 by chance or simply as a result of the action of the laws of 

 physics and chemistry. The formation of enzymes required 

 a definite orientation of the process of the evolution of 

 matter, it required selection, the destruction of all ' un- 

 successful ' combinations and the retention for further evolu- 

 tion of only those systems in which the catalytic apparatus 

 fulfilled its biological function most rationally. 



This evolution of enzymes is still taking place to some 

 extent. It must, however, be pointed out that the basic forms 

 of construction of catalytic systems were already elaborated 

 at what, comparatively speaking, was a very early stage in 

 the establishment of life and its further development. No\va- 

 days, therefore, even in the most poorly organised of con- 

 temporary living things, the individual enzymes are present 

 as fairly highly-developed formations. 



