66 PHYSICAL CHEMISTRY IN BIOLOGY. 



tested with i-amyl alcohol and n-butyric acid or the corresponding 

 ester. It was shown that the reaction took place in the insoluble phase 

 (enzyme). From the formula alcohol + acid <= ester + water, it follows 

 that when the molecular concentrations of alcohol, acid, ester and water are 

 designated C A , C s , C E , C w , the reaction velocity of the ester forma- 

 tion for a homogeneous system is -~ = ki.C A .C s k2-C E .C w (see page 53), 



dx 

 which equation can be simplified to =ki.C s k 2 .C E as the alcohol 



and water were in excess and their concentration considered as con- 

 stant and included in the constants ki and & 2 - At equilibrium we 



have kiC s =k2C E or ~-=-^==K (page 53). It follows that the same 

 #2 C s 



equilibrium is attained irrespective of whether we start with alcohol -f 

 acid, or ester +H 2 O. The equilibrium is also independent of the ante- 

 cedents as well as the quantity of enzyme. 



On comparing the equilibrium constants (K) which are obtained with dif- 

 ferent quantities of ester or acid, it is shown that in the above equation \/C E 

 must be introduced instead of CE in order to obtain constant values for K. In 

 the saponification of the ester the reaction velocity is proportional to \/(7j, 

 and not CE> According to DIETZ this is due to the fact that the system is a 

 heterogeneous one, and that only that part of the ester which is absorbed by 

 the solid phase (enzyme) takes part in the reaction. The velocity constant of 

 the ester formation is shown to be proportional to the quantity of enzyme. 



According to what was stated above (page 56), the equilibrium in a reversible 

 reaction must be independent of the nature of the catalyst. This was not the 

 case in DIETZ 's experiments. With picric acid as the catalyst another equilib- 

 rium was obtained than with the pancreas enzyme. With the acid as catalyst 

 the equilibrium was moved toward the direction of the ester. While this 

 action is not understood it may perhaps be explained by the fact that the 

 system in one case was homogeneous and in the other case heterogeneous. 



Similar observations that the enzymotic end-condition can be dif- 

 ferent from the stabile end-condition of the same system have previously 

 been made by TAMMANN/ but in these cases generally so-called false 

 equilibrium existed, which, for example, by the addition of more enzyme 

 changed, so that the cleavage proceeds further. These false equilibria 

 are generally caused by the enzyme being destroyed or put out of 

 action in other ways. In DIETZ'S experiment the equilibrium was true 

 in every regard, as this condition could be attained from both sides and 

 was independent of the quantity of enzyme. 



Specificity of Enzyme Action. It has been known for a long time 

 that a great difference exists in regard to the action of enzymes in the 

 sense that different enzymes act only upon certain classes of bodies 



1 Zeitschr. f. physiol. Chem., 16, 271, 1892. 



