environment to pH 12 (Figure 3) prior to conducting the procedure eliminated measurable enzyme activity.
In addition to changes in temperature and pH, the concentrations of enzyme and substrate had an effect on enzyme activity.
Substrate concentration was adjusted by altering the proportions
of substrate (H2O2) and water that are added to the reaction, as
described in Table 1.
The temperature increase was nearly double that observed at
baseline (Figure 4) when substrate concentration was doubled.
Likewise, when the yeast suspension containing the enzyme was
diluted, the temperature increase was substantially less (Figure 5
and Table 2). In both cases, the change in enzyme activity, as
measured by temperature increase, is directly proportional to the
adjustment in substrate or enzyme concentration.
Enzyme activity indirectly measured by increase in temperature followed a standard enzyme kinetics pattern as expected. We believe
that the laboratory procedures presented here resolve several challenges for the teaching of enzyme kinetics in the introductory biology laboratory. First, the procedures are simple and inexpensive.
The required equipment and supplies can be easily obtained, and
Figure 2. Effect of elevated temperature on the activity of yeast
peroxidase. When yeast is heated to 100°C prior to conducting
the enzymatic reaction, no enzyme activity is observed. Circles:
baseline reaction. Squares: yeast heated to 100°C.
Figure 3. Effect of increased pH on the activity of yeast
peroxidase. When pH is adjusted higher than optimal for this
reaction, minimal enzyme activity is observed. Circles: baseline
reaction. Squares: pH 12.
Figure 5. Effect of enzyme concentration on the activity of
yeast peroxidase. Reducing concentration of enzyme results in
a reduction in enzyme activity. Circles: baseline reaction.
Squares: reduced enzyme concentration.
Figure 4. Effect of substrate concentration on the activity of
yeast peroxidase. Increasing concentration of substrate results
in an increase in enzyme activity. Circles: baseline reaction.
Squares: increased substrate concentration.