Dissociation of Dibasic Acids

The first practical model for the pH dependence of enzyme catalysis was proposed by Michaehs (Michaehs Davidsohn, 1911). The pH behavior of many enzymes can be interpreted as a first approximation in terms of this model, in which only two ionizable groups are considered. 

The active site of an enzyme is represented as a dibasic acid, with two nonidentical acidic groups (Adams, 1916 Michaehs, 1922 Brockelhurst, 1994). 

With the dissociation constants defined as shown in this scheme, the concentrations of ah forms of enz5mie can be represented in terms of hydrogen-ion concentration  

The constants and J b are termed molecular dissociation constants to distinguish them from the group dissociation constants (JTi-iir,). Only the molecular dissociation constants can be measured experimentally, although evidence can be obtained indirectly on the magnitude of group constants (Dixon, 1976). 

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