17:4/ Enzyme Kinetics of Hydrolytic Reactions 



327 



This equation also predicts a straight line; its graph is also called a 

 Lineweaver-Burk plot. It is illustrated in Figure 7b, where xJV is 

 plotted against x. It is seen that the best points, obtained at large x, 

 are now spread out over a major part of the graph instead of being 

 cramped near the axis. 



The strongest point of the foregoing Michaelis-Menten formulation is 

 that it is the simplest theory which can be fitted to the reactions of most 

 hydrolases. It also fits the reactions of several other types of enzymes. 

 Its weakest point is that the intermediate complex has not been directly 



1/1/ 



x/v 



Slope = \/V max 



K^/V mox 



(b) 



Figure 7. (a) Lineweaver-Burk plot of the hydrolysis of 

 sucrose by sucrase. (b) Modified Lineweaver-Burk plot. 

 After F. M. Huennekens, "Biological Reactions: Measurement 

 and General Theory," Technique of Organic Chemistry, Vol. 8, 

 Investigations of Rates and Mechanisms of Reactions, S. L. Friess and 

 A. Weissberger, eds. (New York : Interscience Publishers, Inc., 

 1953). 



observed for most reactions; it could easily be an oversimplification. In 

 spite of these uncertainties, this type of kinetics is the basis for many 

 studies. Almost all enzyme kinetics are described in the language of 

 intermediate complexes and Michaelis constants. 



4. Action of Inhibitors 



Many enzyme reactions have been studied in part through the use of 

 inhibitors. Specific inhibitors are useful for determining the role of 

 particular enzymes. Other inhibitors (such as para-chloro-mercuri- 

 benzoate, PCMB) are useful in determining the activity of certain 

 groups (for example, sulfhydryl groups) in the enzyme activity. In this 

 section, the action of inhibitors for systems obeying Michaelis-Menten 

 kinetics will be analyzed. 



