Enzymic Reactions in Stationary 

 Open Systems 



A. G. PASYNSKlI 



A. N. Bakh Institute of Biochemistry of the Academy of Sciences of the U.S.S.R., Moscow 



The constant exchange of matter and energy with the surrounding medium 

 is characteristic of life in all its forms. In this respect all living organisms are 

 so-called 'open systems'. As A. I, Oparin has discussed in detail [i], from the 

 evolutionary point of view the emergence of the simplest forms of Ufe in the 

 form of biological open systems must have been preceded by the formation of 

 non-hving, chemical, open systems in which the spatial-temporal organization, 

 co-ordinating the chemical reactions within the framework of a definite struc- 

 ture, had not yet led to the self- reproduction and self-maintainance of the system. 

 Investigations of the thermodynamics [2, 3] and kinetics [4] of irreversible 

 stationary chemical processes in open systems have, in recent years, brought 

 about a considerable development in physics and chemistry; obviously the 

 general properties of catalysed chemical reactions (especially enzymic ones) in 

 open systems must be of practical interest to biochemists as well [5]. 



The study of enzymic reactions has hitherto been mainly limited to reactions 

 in enclosed systems in which the concentration of reacting substances and the 

 rate of the reaction changed continually with time until the process finished. On 

 the other hand, enzymic reactions in any cell in the hving body take place under 

 conditions of constant diffusion of metabolites in the cell and transport of the 

 products of the reaction into the surrounding medium, i.e. under the condi- 

 tions of an open system. In contrast to reactions in an enclosed system, a 

 stationary state may be established in an open system (it differs in principle in 

 many ways from the thermodynamic equilibrium in an enclosed system [5]). 

 Owing to the continual exchange with the medium this may be maintained 

 dynamically for as long as one likes. In the present work, which was done in 

 collaboration with V. P. Blokhina, the stationary state of an enzymic reaction 

 was studied, using as an example the simplest reaction of enzymic oxidation of 

 ascorbic acid A-D in the presence of peroxidase. 



Let us suppose that substance A is continually coming in from the medium 

 with a coefficient of transfer (diffusion or permeability) of Ko at a concentration 

 S, and that the product of the reaction, D, is continually leaving the sj'stem 

 with a coefficient of transfer of Kz at a concentration Z. In this case we obtain 

 an open system 



Ko ': ^ \K, 

 S A . D ► Z 



: K' 



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