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.