CATALYSIS USING ENZYMES IN PINEAPPLE

PURPOSE

In this experiment, students investigate methods for altering the functioning of an enzyme catalyst.

DESCRIPTION

This experiment is appropriate for use in a general or first-year college-prep class while studying catalysis. It could also be used in a course studying organic and biochemistry and, with appropriate modifications, with younger students. Pineapple contains an enzyme that hydrolyzes certain proteins called gelatins. In this experiment, students add pineapple, which has been subjected to various treatments, to gelatin to determine if the treatment has altered the enzyme's activity.

TIME REQUIRED

One lab period plus 15 minutes the next day to observe the samples.

MATERIALS

Chemicals

gelatin - one 6 oz box of Jell-O Brand gelatin dessert will be enough for 10 samples
canned pineapple slices
fresh pineapple*
sun-dried pineapple rings*

Equipment

150-mL or 250-mL beakers*
stirring rods*
hot plates slotted spoon or tongs
2-L beaker*
1-L beaker*
100-mL graduated cylinder
balance

*See Modifications/Substitutions

HAZARDS

Caution should be used in preparing the pineapple pieces and in heating and transferring both the water and the pineapple. Students should not eat the samples unless equipment used only for food preparation has been used throughout the experiment and the samples have been chilled in a refrigerator used solely for food.

MODIFICATIONS/SUBSTITUTIONS

1. Frozen pineapple may be substituted for the fresh pineapple if fresh is not available. Freezing does not denature the enzyme.
2. Sun-dried pineapple is available at some grocery stores and at health food stores.
3. If samples are to be eaten following the experiment, equipment that has never been used for chemical experimentation should be used. The following equipment could be substituted for normal labware: clear plastic cups, popsicle sticks, 2-qt saucepan, 1-qt jar, and measuring cup.

PROCEDURE

1. Cut each slice of drained canned pineapple into four approximately equal pieces. Peel and cut the fresh pineapple into slices and pieces which are about the same size as the canned pineapple pieces. Cut the dried pineapple into pieces the same size as the others.
2. In a 2-L beaker, heat approximately 500 mL of water to boiling for each set of 10 samples.
3. Weigh out ten 17-g samples of gelatin and place one sample in each of ten 150-mL or 250-mL beakers.
4. Carefully add 40 mL of boiling water to each sample. Stir until dissolved. With stirring, add 40 mL of cold water to each sample.
5. Begin to heat another 500 mL of water in the 2-L beaker on the hot plate.
6. Label ten beakers as follows:

2 - canned pineapple

2 - sun-dried pineapple

2 - fresh pineapple

1 - fresh pineapple heated 0.5 min.

1 - fresh pineapple heated 1.0 min.

1 - fresh pineapple heated 1.5 min.

1 - fresh pineapple heated 2.0 min.

7. Place appropriate pieces of pineapple into each of the first six beakers of gelatin. At the same time, put a 1-L beaker containing the remainder of the fresh pineapple in the beaker of boiling water on the hot plate and start to time immediately. At the appropriate times, remove a piece of the pineapple and put it in the corresponding beaker.
8. Place all the samples in a cool place. A refrigerator will hasten the jelling process and make it easier for students to distinguish between samples that have jelled and those that have not. Observe the samples the next day.

DISPOSAL

Discard the remains of the pineapple and the gelatin in the locally approved manner for food wastes.

DISCUSSION

All living cells produce enzymes which catalyze metabolic reactions. An enzyme is an organic catalyst that alters the rate of a specific chemical reaction but which remains unchanged at the conclusion of the reaction. Enzymes are classified according to the substrate on which they function or the reaction they catalyze.

The enzyme that is investigated in this experiment is one that is produced in pineapple and hydrolyzes certain kinds of proteins called gelatins. The gelatin used in this experiment is derived from skin, bones, and/or connective tissue of animals. These proteins, when dissolved in hot water and allowed to cool, form a semi-solid or gel state; hence the name gelatin. Hydrolyze, here, refers to breaking up the protein polymer in such a way as to prevent its forming this gel state. The manufacturers of gelatin containing desserts customarily warn the consumer against adding fresh or frozen pineapple or kiwifruit to the dessert to prevent this reaction.

The hydrolyzing enzyme from pineapple is denatured by heat. Denature, here, means to alter in such a manner that the enzyme is no longer able to catalyze the reaction. Enzymes can also be denatured by changes in pH, subjection to detergents or radiation, etc.

TIPS

1. This experiment could be done as a demonstration.
2. Students could also study the effects of pH, detergents, and microwave radiation as a means of denaturing the enzymes. Perhaps fresh pineapple could be allowed to ferment to see if the fermentation process altered the enzymes' function.
3. This investigation could be used with elementary age students if the teacher demonstrated the preparation of the gelatin and the pineapple and simply let the students mix the two together.

REFERENCES

Hechtlinger, A., Biochemistry Units for the High School Biology Teacher, Parker Publishing Co., Inc., West Nyack, NY, 1973, p. 93.
This reference mentions, very briefly, the possibilities of using pineapple to study enzymes.

Lehninger, A.L., Principles of Biochemistry, Worth Publishers, Inc., New York, 1982, p. 158.
This reference describes, in some detail, the chemical make-up of enzymes and their functions. Any good, college level biochemistry text would be an applicable substitute.