374 THE FIRST ORGANISMS 



The origin of the co-ordinated networks 

 of reactions : the origin of the 

 first organisms. 



Enzymes are, however, only the elementary and simplest 

 form of organisation of protoplasm, its separate working 

 mechanisms. 



The extreme specificity of protein enzymes means that 

 each of them can only form intermediate compounds with a 

 definite very narrow group of substances and can only cata- 

 lyse strictly determinate individual reactions. However, the 

 separate reactions catalysed by the different enzymes cannot 

 of themselves, in isolation, serve as a basis for the process of 

 life. Their biological significance becomes manifest and well 

 defined only by virtue of their strict co-ordination with all 

 the other chemical processes of the living body ; their place 

 in the general network of reactions in open systems is only 

 maintained when they are included as essential links in a 

 long chain of metabolic processes. 



Hundreds and thousands of enzyme proteins play their 

 parts in each vital process, let alone metabolism as a whole. 

 Each can catalyse only one or a very limited number of 

 reactions, and it is only when taken together, when their 

 actions are unified in a definite way, that they constitute 

 the orderly sequence of phenomena which forms the founda- 

 tion for the process of life. 



By using chemically individual enzymes isolated from 

 living organisms one may produce, under laboratory condi- 

 tions and in isolation, separate biochemical reactions which 

 are links in the metabolic chain. This enables us to unravel 

 the complicated skein of chemical reactions which make up 

 metabolism, in which thousands of individual chemical 

 reactions are carried out ; to dismember metabolism into 

 its constituent stages ; to analyse not only the composition 

 of living bodies, but also the chemical processes which are 

 carried out in them and on which vital phenomena depend. 



The great service of A. N. Bach (Bakh)^^ to biochemistry 

 was that, as early as the end of the nineteenth century, he 

 showed, in his study of the chemistry of respiration, for 

 example, that this phenomenon could not depend on the 



