Effect of pH on Enzyme Activity

Biochemical Engineering

Problem Statement: Consider an enzyme reaction mechanism where substrate S can be reversibly protonated and only the protonated form (SH+) can reversibly combine with an enzyme E to form an active complex (ESH+), which then irreversibly leads to a product PH+. 

            ki
  S + H+ <------> SH+
            k-i

             k1            k2
  SH+ + E <------> ESH+ ------> E + PH+
             k-1
  1. Derive the rate expression v=dp/dt as a function of S, H, P, and E0. Set up the equations; solve them only when time permits. The following is the eventual expression, provided here in case you think you need it to answer questions in the next steps. 
    v=vm*s/(Km*Ki/H+s)

    Solution:

    See the following files that discuss the effect of pH on enzyme activity ("Mechanism #1, Acid Enzyme").

    Note that the rate expression is different from Eqn (3.45) of Shuler & Kargi.

  2. Is the reaction rate higher in acidic or alkaline condition? Roughly sketch a plot of reaction rate versus pH.

    Solution:

    Higher reaction rate in acidic conditions.

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Biochemical Engineering -- Effect of pH on Enzyme Activity
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