ORIGIN OF THE FIRST ORGAiNISMS 379 



isation which is very labile and adaptable, but at the same 

 time very efficient. The process of extracellular fermentation 

 is not associated with any protoplasmic structure ; the whole 

 process simply takes place in a solution of the enzymes of the 

 zymase complex. In the cells of contemporary organisms, on 

 the other hand, the spatial organisation of their protoplasm 

 exercises a great, and sometimes decisive, influence on the rate 

 and direction of the enzymic reactions on which its metabol- 

 ism is based. We now know that the enzymes of cells are 

 present, for the most part, in an associated state on proto- 

 plasmic surfaces and various cellular structures. ^^ 



The investigations carried out in the Institute of Bio- 

 chemistry of the Academy of Sciences of the U.S.S.R. (A. 

 Kursanov,^" N. Sisakyan, B. Rubin and A. I. Oparin*^) have 

 shown that the degi^ee of association of the enzymes with the 

 structures mentioned has a decisive effect not only in deter- 

 mining changes in the rates of the reactions catalysed by the 

 enzymes, but also in displacing the dynamic equilibrium of 

 the chemical processes towards a predominance of break- 

 down or synthesis. This, naturally, is of paramount import- 

 ance for the self-preservation and growth of the whole living 

 system. Phenomena of this sort cannot be explained on the 

 basis of the laws which have been established for closed 

 systems. As was shown in the previous chapter, however, in 

 open systems (as distinct from enclosed ones) a catalyst may 

 alter the stationary concentrations of the reacting substances, 

 i.e. it may displace the experimentally determined, dynamic 

 ' equilibrium ' of the process. 



This sort of influence of the protoplasmic structures on 

 the rate and direction of the enzymic reactions of the meta- 

 bolic network leads to a very intimate and critical connection 

 between the metabolism and the conditions of the external 

 medium. It very often happens that a factor which has a 

 very weak or hardly noticeable effect on the activity of isolated 

 enzymes will produce a radical displacement of the equi- 

 librium betw^een breakdown and synthesis, by altering the 

 associated power of the protein structures of protoplasm, 

 which are very sensitive in this respect. 



According to contemporary cytological evidence^^ a very 

 considerable part of the cytoplasm, up to 50 per cent of its 



