What is guaiacol and why is it used in the peroxidase enzyme experiment?

Guaiacol is a color-changing indicator that becomes progressively more yellow-orange as the peroxidase enzyme reaction progresses. It allows researchers to visually track enzyme activity by observing the color intensity change over time, making it possible to quantify the relative reaction rate by comparing observed colors to a standard reference.

How do you prepare the substrate and enzyme solutions for the baseline peroxidase reaction?

The substrate is prepared by combining 7 mL distilled water, 0.2 mL guaiacol, and 0.3 mL of 0.1% hydrogen peroxide in a test tube. The enzyme solution contains 6.0 mL distilled water and 1.5 mL turnip peroxidase. Both are mixed separately by four inversions, then combined and mixed again before timing begins.

What is the optimal pH range for peroxidase enzyme activity?

The optimal pH for peroxidase enzyme activity is typically in the range of 6 to 7, representing a mid-range neutral pH. As pH becomes more basic, enzyme stability decreases and reaction rates drop significantly. Testing pH levels 3 through 8 reveals this optimal range through color intensity measurements.

Why does peroxidase enzyme activity decrease at high temperatures?

At high temperatures, the peroxidase enzyme begins to denature, losing its three-dimensional structure and catalytic ability. Above 45 degrees Celsius, the enzyme becomes increasingly unstable and produces little to no color change. At 60 degrees Celsius, the enzyme is sufficiently denatured that the reaction does not occur.

What is the optimal temperature for peroxidase enzyme activity in this experiment?

The peroxidase enzyme shows maximum efficiency around 45 degrees Celsius in this experiment. This temperature balances sufficient molecular energy for catalysis with enzyme stability. Below this temperature, reaction rates are slower, and above it, enzyme denaturation significantly reduces activity and color production.

How does temperature affect enzyme reaction rates at low temperatures?

At low temperatures, such as in an ice bath, the reaction rate slows or stops because there is insufficient molecular energy for the enzyme to catalyze the reaction effectively. Reduced thermal energy limits enzyme-substrate collisions and the rate of product formation, resulting in minimal or no observable color change.

How do you quantify enzyme activity changes in this peroxidase experiment?

Enzyme activity is quantified by graphing color intensity changes against time or experimental conditions. The baseline reaction establishes a reference rate measured in color units over five minutes. Comparing pH and temperature treatments to this baseline reveals how environmental factors affect reaction rates and enzyme efficiency.

Enzyme Activity

Concepts Instructor Prep Student Protocol

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European explorers had adequate knowledge, skills and equipment, but why didn't they reach the New World until the end of the 15th century? You'll be surprised to learn that the answer to this question is related to the small biological molecules called enzymes, that act as catalysts.

What is a catalyst? It is a substance that enables a reaction to occur faster, using less energy. If you plotted a graph of the energy needed for an uncatalyzed biological reaction, it would look something like this. This height represents the activation energy, which is the minimum amount of energy needed for the reaction to proceed. Enzymes, working as a catalyst, provide an alternate reaction pathway, with a lower activation energy.

So, how do enzymes actually work? Most enzymes are proteins. The part of their structure which interacts with the molecules they catalyze, is called the active site, which has affinity for only certain substrates and won't bind with others. When the correct substrates enter the active site, the enzyme changes its shape to attain a higher affinity configuration. This transition state facilitates the reaction and converts the reactants into products. The enzyme, however, has a lower affinity for the products so it releases them and returns to its original shape, ready to repeat the same process. This is an example of a catabolic enzyme because it took a single substrate and broke it to form multiple products. The opposite of this, is the anabolic enzyme, which takes two substrates and joins them together to make a larger product.

There are numerous other ways that enzymes function. For instance, this enzyme transfigures a single substrate into a new shape. Whereas this one, transfers part of one substrate, onto another. Some enzymes cannot catalyze reactions on their own and require cofactors or coenzymes in order to catalyze their reaction.

So, you might be wondering, how does all this relate to the 15th century voyages? At that time, sailors didn't have access to fresh produce containing vitamin C, a coenzyme essential for collagen synthesis. Because of that, the sailors would develop scurvy, a vitamin C deficiency disease, which was often fatal. They solved this problem by pickling vitamin C-rich fruits and vegetables. Pickling reduced the pH of the food, which prevented the activity of microbial enzymes, responsible for rotting them. Therefore, destruction of microbial enzymes and the saving of an essential coenzyme, played a major role in the success of long expeditions.

In this lab, you can quantify how different conditions affect enzyme function, by assessing the reaction rate, the amount of product made, per unit time. You'll first measure the baseline reaction rate at a standard room temperature and neutral pH. The rate will increase at the beginning until all of the enzyme molecules are completely saturated with the substrate. And then, the catalysis will reach a steady level as the enzymes are busy continuing the cycle of binding substrate, catalysis and release. Once the baseline reaction rate has been established, it can be used as reference point for other conditions. The enzyme that you'll work with in this lab is turnip peroxidase. You'll evaluate its activity under varying values of temperature and pH.

Print Procedure Steps

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Baseline Peroxidase Enzyme Experiment
- To begin, the baseline for the peroxidase enzyme reaction must be determined. Make the substrate by adding 7 mL of distilled water to a clean test tube and then add 0.2 mL of guaiacol. Note: Guaiacol is a color-changing indicator that becomes more yellow-orange as the enzyme reaction progresses.
- Next, add 0.3 mL of 0.1% H2O2.
- Using a marker, label the test tube substrate and then cover the tube with a piece of sealing film.
- Holding the cover in place, invert the tube four times to mix the tube contents.
- In a second test tube, add 6.0 mL of distilled water and 1.5 mL of turnip peroxidase and label this tube “Enzyme”.
- Cover this tube with a new piece of sealing film and mix these solutions by four inversions as previously described (step 4).
- When both tubes have been mixed, place a timer on the bench, next to the test tube rack, then pour the contents from the substrate tube into the enzyme tube, being careful not to spill any liquid.
- Next, pour the entire volume from the enzyme tube back into the substrate tube to thoroughly mix the solutions and cover the substrate tube with another piece of sealing film.
- Put the test tube in the rack and start the timer.
- Observe the color in the substrate tube at 0, 1, 2, 3, 4 and 5 minutes, post-mixing.
- To quantify the relative change in color and the rate of the reaction, match the observed color to the closest color in the standard. NOTE: Taking a photo of the observed color intensity at each sample point may make it easier to record the results.
- Record the colors you see in the table. Click Here to download Table 1
Investigating the Effect of pH on Peroxidase Activity
- HYPOTHESES: In this exercise, the experimental hypothesis is that the reaction rate will reach a maximum or optimum at a mid-range neutral pH and that these rates will be higher than or roughly equal to the baseline rate. The null hypothesis is that there will be no differences in the reaction rates between the baseline and the pH treatments.
- First, label six clean test tubes for each of the six pH buffer levels 3 - 8 and the word “Enzyme”.
- Next, add 6 mL of the corresponding pH buffer solutions provided by your instructor to each of the test tubes.
- Then, add 1.5 mL of the turnip peroxidase to each tube, being careful not to contaminate the dropper with the buffer solution.
- Cover the enzyme tubes with sealing film and gently invert each tube to mix the tube contents.
- As described in the baseline reaction experiment, make the substrates for these reactions by adding 7 mL of distilled water, 0.2 mL of guaiacol and 0.3 mL of 0.1% H₂O₂to six new clean test tubes.
- Next, label six additional clean test tubes with the pH levels 3 - 8 and the word “Solution” and get a timer ready.
- Working quickly, pour a substrate tube and a pH tube into the corresponding solution tube. Repeat this step for each of the different pH levels.
- Then, cover the tubes with sealing film and mix each tube with four inversions. Place each tube in a tube rack, as they are mixed.
- Observe the color in each tube at time 0 and immediately start the timer. Continue to observe the color in each tube at every minute interval, up to 5 minutes.
- At each interval, use the color code in the standard to record the observed colors in your table.
Investigating the Effect of Temperature on Peroxidase Activity
- HYPOTHESES: In this exercise, the experimental hypothesis is that the reaction rate will reach an optimum above room temperature, or 23 °C, but below enzyme denaturation rate and that this maximum will be higher than the baseline rate. The null hypothesis is that there will be no differences in the reaction rates between the baseline and the temperature treatments.
- Fill an 800 mL beaker about halfway to the top with ice and pour cold water into the beaker to create an ice bath. Label this beaker as “Ice”.
- Then, label four new 600 mL beakers with the same temperatures as your substrate tubes and add 150 mL of tap water to each.
- Using a hot plate and a thermometer, bring the beakers to 25, 35, 45 and 60 °C, as per their labels.
- Prepare five more pairs of substrate and enzyme tubes, as described for the baseline reaction, using distilled water in the enzyme tube, instead of a pH buffer.
- Label the substrate tubes as “Ice”, “25 °C”, “35 °C”, “45 °C”, and “60 °C”.
- When all of the water baths have reached their appropriate temperatures, mix the substrate and enzyme solutions together by first pouring each substrate tube contents into an enzyme tube and then pouring the enzyme tube contents back into the substrate tube.
- Cover the substrate tubes with sealing film and observe the colors at time 0.
- Then, stand the tubes in their corresponding beaker baths, based on the temperature label each tube was given and start a timer.
- For each 1-minute interval, remove the tubes from the water and record their color, using the stabdard as a reference.
- Then, place them into their baths until each time point, up to 5 minutes, has been recorded.
Results
- To determine the baseline for the reaction, graph the change in color intensity against time. NOTE: The number of units that the color increased by over the 5-minute time period will serve as the baseline rate of reaction for relative comparison.
- Now graph the difference in color intensity against the pH levels used in the first experiment.
- Add in the baseline for comparison and then determine whether the optimal reaction rate was higher than, lower than or equal to the baseline.
- Using this graph, determine the optimum pH for the reaction. Note: The reaction may not occur at every pH. The optimum pH for the peroxidase enzyme is typically in the range of 6 - 7. By exposing the enzyme to a substrate with different levels of pH, you will notice a drop-off in the reaction rate as the pH of the enzyme becomes more basic, making the enzyme more unstable.
- Finally, graph the difference in color intensity over time for the different temperatures used in the second experiment, using the same baseline for comparison.
- Using this graph, determine the optimum temperature for the reaction and compare it to the baseline. NOTE: The reaction may not occur at every temperature. In this experiment, the reaction appears most efficient around 45 °C, and above this, the peroxidase enzyme begins to denature. For this reason, it should not produce a color change in the 60 °C beaker. The reaction rate will also slow or stop in the ice bath, as there is not enough energy for the enzyme to catalyze the reaction.