Easy Enzyme Experiment: Potato Catalase

Catalase enzyme formed the bubbles in the two tubes on the right.  The tubes contain extracts from beef muscle, kidney, and liver from left to right. 

In a post awhile back we discussed the enzyme catalase and its presence in animal tissues such as liver, kidney, and muscle.  Catalase was and is found to be extremely abundant in the liver, a reflection of the livers cleansing function.  It is also present, but much less so, in the kidneys, also a reflection cleansing function.  Muscle tissue however had no detectable catalase due to the fact that it is not a cleansing organ, waste products from the muscles are rather filtered and cleaned by the liver and kidneys.  Catalase also has been found in plants, where its presence is often mysterious.  Plants of course are not producing waste products similar to what animals produce, so why would they need catalase?  We can discover the answer partially by simply understanding the function of catalase.

This is what catalase does in general:

Hydrogen Peroxide + Catalase → Water and Oxygen

Hydrogen peroxide is a highly oxidative molecule, meaning it causes processes similar to rusting to occur.  Metals rust as they react with oxygen and oxidative molecules cause rusting to occur.  Similar “rusting” or oxidative reactions can occur in plant or animal tissues if oxidative molecules are present.  This is why anti-oxidants are such a big deal, they prevent tissue from oxidizing by getting rid of oxidizing molecules such as hydrogen peroxide.  Catalase is such an anti-oxidant molecule.  Catalase also converts reactive oxygen, which also oxidizes, into hydrogen peroxide and then into harmless water and oxygen.  (Of course I have simplified these reactions, so chemists, refrain from complaint!)  At the end of a reaction catalase is preserved and available to repeat the reaction over again with more oxidative molecules.  Amazingly, one catalase enzyme can repeat these reaction up to 40 million times in one second!

Another catalase reaction:

Reactive Oxygen + Catalase → Hydrogen Peroxide + Catalase → Water and Oxygen

In animals, such as us, oxidative molecules are most often produced through our metabolizing of food molecules.  So the presence of catalase makes sense.  Plants do not eat, so why would they need catalase?  If we study the process of photosynthesis we may come across a term called photorespiration.  Photorespiration simply is when a plant receives too much light and not enough water.  As a result, the plant can produce large amounts of hydrogen peroxide which can kill the plant.  Fortunatly, catalase prevents the accumulation of hydrogen peroxide by converting it to water and oxygen, and so saves the plant from oxidative damage.

A Simple Catalase Experiment Using Potatoes:
Some plants such as potato and spinach have very high levels of catalase, far higher they they would likely ever need to prevent photorespiration damage.  Why that is, no one seems to know. Scientists have had many ideas and have researched the question for almost 100 years but no one can figure it out.  But it makes isolating the catalase enzyme very inexpensive and easy if you want to run a simple experiment.  The following is a simple enzyme experiment anyone can run.
Materials:
Potato
Test tube or other small container
Hydrogen Peroxide

1. Cut up a potato and mash it.  Do not cook it, cooking will break down the enzyme so it won’t work.

2. Place the mashed potato in a test tube or other small container.

3.  Add hydrogen peroxide.  If there is catalase present foam should be produced.

The foam produced is a result of catalase converting hydrogen peroxide into water and oxygen, the bubbles are filled with this oxygen.  The more bubbles produced the faster catalase is carrying out this reaction, or the more catalase present.  The above would be considered the control for the experiment and simply indicated the presence of catalase in the potato.  Tests can be preformed to determine the effects of different conditions on the enzyme function.  By adding baking soda to the potato, a high pH or basic molecule, will change the pH and have an effect on how well catalase functions.  To another test tube, add vinegar to the potato which will lower the pH, making it acidic also having an effect.  Also try freezing or cooking the potato before adding hydrogen peroxide to determine effects.  Remember, the more foam produced the better the catalase enzyme is working.  Less foam means it is not working as well, and no foam means it is not working at all.  Test it out and see what you find.  

Potato catalase experiment.  The boiled tube (left) produced no bubbles indicating catalase has been degraded by the heat.  Room temperature tube (middle) produced the most bubbles indicating catalase is highly functional at this temperature.  The tube kept on ice (right) produced fewer bubbles indicating the lower temperature slowed down the catalase enzyme.