Effects of pH

• 8 mM DOPA in citrate buffer adjusted to pH values of 3.6, 4.2, 4.8, 5.4, 6.0,
• 6.6, 7.2, and 7.8
• Enzyme extract
• Spectrophotometer and cuvettes
• Stopwatch

1. Set up a series of test tubes, each containing 2.5 mL of 8 mM DOPA, but adjusted to the following pH values: 3.6, 4.2, 4.8, 5.4, 6.0, 6.6, 7.2, and 7.8.
2. Begin with the tube containing DOPA at pH 3.6, and add 0.5 mL of the diluted enzyme extract which will convert 10 micromoles of DOPA in 3–5 minutes. Start timing the reaction, mix by inversion, and insert into the spectrophotometer. Note the time for conversion of 10 micromoles of DOPA.
3. Repeat step 2 for each of the indicated pH values. Complete the following table:
   
   
   
4. Plot pH (x-axis) versus reaction velocity (y-axis).