112 



4. SUBSTRATE INHIBITION AND PRODUCT INHIBITION 



and Webb, 1944; Heppel and Hilmoe, 1951; Bloch-Frankenthal, 1954), 

 aminoacylase I (Mounter et ah, 1958), sucrose transglucosylase (Neely, 

 1958), diphosphoglyceromutase (Joyce and Grisolia, 1959), and p-hydroxy- 

 phenylpyruvate oxidase (Zannoni and La Du, 1959). 



Possible Mechanisms Involved 



Before considering the kinetics of substrate inhibition it is helpful to 

 summarize the most important mechanisms by which this type of inhibi- 

 tion may be produced. These mechanisms are schematically illustrated 

 in Fig. 4-1. 



TYPE A 



_Bz:®. 



TYPE B 



TYPE C 



--%r 



A ^^ 



TYPE .^ ^ ^-~ 



TYPE E 



Fig. 4-1. Postulated mechanisms of substrate inhibition. In 

 type A it may be noted that groups 1 and 2 may be identical. 

 In type B the enzyme sites must be close enough so that inter- 

 ference occurs. In type E the binding of the second substrate 

 molecule is generally less strong due to the poorer fit. See 

 the text for explanation. 



