The effect of pH on enzyme activity
Enzymes are active only within a limited range of pH. But
the limits may be wide, e.g. pH 5 to 10, or narrow, e.g. over
1 pH unit. Within the range there will be an optimum at
which the maximum activity (the highest value for Vmax) is
attained: this could be a short range in itself. The activity
can also be affected by the nature of the buffer used. There
could be a discontinuity in activity over the pH range tested
because of the use of different buffers. Alternative buffers
for a given pH should be tested.
The effect of pH is generally tested at high substrate
concentration. However, if tested at low concentration, it is possible that the value of v may change with pH because of
an effect not on Vmax, but on Km. For standard enzyme
assays, a value of pH is chosen that is close to the optimum,
unless some other component of the assay mixture cannot
operate at that pH.