ENZYME KINETICS 



Steady-State measurements because they are less difficult to 

 perform than transient-state measurements. The fact that a 

 reaction follows a certain rate equation does not prove a certain 

 mechanism is operative, but it does eliminate many mechanisms 

 from consideration. However, if several mechanisms which 

 yield a given rate equation are considered carefully, it may be 

 possible to devise further experiments which will distinguish 

 between the possibilities. 



It is interesting to note that rate equations derived for very 

 simple mechanisms may be applicable to reactions that really 

 follow much more complicated mechanisms. This is true since 

 simple rate equations are special cases of the more complicated 

 rate equations which are obtained when certain concentration 

 variables are held constant or experiments are limited to a 

 certain concentration range. For example, at a constant pH 

 and coenzyme concentration the Michaelis-Menten rate equation 

 is applicable to certain enzymatic reactions. However, the 

 fact that the parameters in this equation are dependent on 

 pa and coenzyme concentration shows that the mechanism is 

 more complicated than that postulated by Michaelis and 

 Menten. 



Experimental Methods 



A good deal has been learned about enzyme kinetics with 

 crude preparations, but purity of all substances involved is 

 basic for accurate quantitative studies. Thus detailed kinetic 

 studies must be preceded by research in which the enzyme is 

 isolated, the products of the reaction are identified, and the 

 possible participation of activators or coenzymes is established. 



The success of an enzyme kinetic study is vitally dependent 

 upon the sensitivity, speed, and accuracy of the analytical 

 method. Of the many experimental techniques which have been 

 used to study enzymatic reactions, physical methods are generally 

 more accurate and convenient since they do not require stopping 

 the reaction, and a continuous record of concentration may be 



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