GENERAL PRINCIPLES OF BIOCHEMICAL ENERGETICS 149 



being nourished by negative entropy (Schrodinger). There is nothing here 

 which contradicts the second law of thermodynamics, for in the total 

 system made up of the organism and its surroundings the entropy increases. 

 An organism is made up of one or more cells ; each cell is itself an assembly 

 of open systems which receive free energy and dispose of it. 



As Prigogine (1947) has shown, open systems have some very remarkable 

 properties. 



(1) They tend towards a "stationary state" corresponding to a state of 

 minimum entropy compatible with the conditions of the system. 



(2) The entropy of the system can decrease when the "stationary state" 

 is established. 



(3) If one of the components of the system is modified, the system 

 changes in an opposing direction, revealing a capacity for self-regulation. 



It can be seen that the statiojiary state of "constrained disequilibrium", 

 which is manifest in organisms, with its continual introduction and removal 

 of materials, is quite different from the equilibrium of a reversible reaction. 



Let us take, for example, the case of a monomolecular reversible reaction 



k 



A ^B 



k' 



According to the law of mass action, we may write : 



(^) k ^ ^ ...^ . 



--J- = -,= K (equilibrmm constant) 



[A) k 



When equilibrium is reached, the rates of conversion of A into B, and B 

 into A, are equal. 



If B is constantly removed to a pool Z and if A is constantly replaced 

 from a source of supply S, the flux will be defined as follows : 



k« k kz 



S< >A ^B< >Z 



k' 



ks and kz are the diffusion constants (or "permeabilities"). It can be seen 

 that to define the stationary state we must consider not only the size of the 

 source and the pool but also the equilibrium constant of the reaction itself. 

 In order for the stationary state to be maintained, S and Z must remain 

 constant regardless of subtractions or additions. 



There are many cases in organisms where the equilibrium of a reversible 

 reaction has been upset in one direction or the other. For example, in 

 vertebrates when oxygen is transported, the reversible reaction 



Hb + 0.2 ^ HbO, 



takes place from left to right when the blood passes through the lungs and 

 from right to left when the blood reaches the tissues. 



