Kinetic Analysis

• 8 mM DOPA, pH 6.6
• Enzyme extract, diluted to yield 10 micromoles of dopachrome in 3–5 minutes
• Spectrophotometer and cuvettes
• Stopwatch

1. Prepare a reaction blank in a clean cuvette containing 2.5 mL of citrate buffer and 0.5 mL of enzyme extract. Use this blank to adjust your spectrophotometer for 100% transmittance. Remove the blank and save it.
2. Add 2.5 mL of 8 mM DOPA, pH 6.6, to a clean cuvette.
3. Add 0.5 mL of appropriately diluted enzyme extract. Shake well and immediately insert the tube into the spectrophotometer. Record the absorbance or transmittance as quickly as possible. Designate this reading as time 0.
4. At 30-second intervals, read and record the transmittance until a transmittance value of 10% (absorbance = 1.0) is reached. Complete the following table:
   
   
   
5. Plot time in minutes (x-axis) versus the amount of dopachrome formed (y-axis).