Experiments with enzymes: dehydrogenases. Fun chemistry experiments at home

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Experiments with enzymes: dehydrogenases. Chemical experiments

Entertaining experiments in chemistry

Entertaining experiences at home / Chemistry experiments for children

Let's try to experiment with enzymes from animal tissues. The object of the new study is dehydrogenases, which are involved in the processes of tissue respiration in animals. From the name of these enzymes it is clear that they take away hydrogen atoms from substances. How this happens, you will see a little later, but for now, prepare everything you need for the experience.

This time you will need the following substances: 5 ml of a 0,5% aqueous solution of formaldehyde (dilute pharmacy formalin with water ten times); the same amount of 0,02% aqueous solution of methylene blue (diluted blue ink can be used); the same amount of an aqueous solution of succinic acid, carefully neutralized with baking soda until the release of bubbles stops; 10 ml of vaseline or vegetable oil. You will also need a thermometer and research objects - fresh cow's milk and chicken or rabbit meat.

First, let's see how fresh milk dehydrogenase oxidizes formaldehyde. For this to become noticeable, a solution of methylene blue dye was needed: dehydrogenase will take away a hydrogen atom from formaldehyde, transfer it to an easily recoverable dye, and it will discolor. And formaldehyde is oxidized in this case to formic acid. The dye, discolored after reduction, is easily oxidized by atmospheric oxygen and turns blue again. Therefore, the reaction mixture will have to be isolated from the air with a layer of oil.

Number six tubes. Pour 1 ml of fresh unboiled milk into test tubes 2 and 5, and the same amount of cold boiled milk into test tube 3.

Heat the water in a water bath to 37°C. Add 0,5 ml (about 50 drops) of formaldehyde solution and 5 drops of methylene blue solution to all three tubes. The mixture will turn blue. Pour a little oil into each vial to form a thin insulating layer on the surface, and place tubes 1 and 3 in a water bath. Leave tube 2 at room temperature. Note the start time of the reaction and observe the color change of the solutions. Don't forget to write down the results in your notebook.

As before, we will ask you leading questions. At what temperature does the solution decolorize the fastest?

Does the enzyme retain its activity in boiled milk?

What happens when air is blown through a decolorized solution?

Before checking the correctness of your conclusions, set up another experiment with dehydrogenase, and then consider the results of both experiments.

Animal muscles contain a specific enzyme, succinic acid dehydrogenase. It catalyzes the conversion of succinic acid to fumaric acid with the transfer of the removed hydrogen to a suitable substance, for example, methyleneose blue. This reaction proceeds without the participation of oxygen, as they say, under anaerobic conditions.

Raw chicken or rabbit meat (about 10 g), finely chop and rub on a saucer. Rinse the gruel several times with water on gauze to remove soluble substances. Stir the washed gruel with a triple volume of water, to which table salt is added - about a third of a teaspoon. Pour the diluted slurry into test tubes 4, 5, 6 - 5 ml each. Immerse tube 4 in a boiling water bath for five minutes and cool to room temperature. Then add 4 ml of succinic acid solution and 5 drops of methylene blue solution to test tubes 0,5 and 10, and add 6 ml of water and 0,5 drops of dye to test tube 10. Add a little oil to each bottle to isolate the mixture from air. Having traced the color change, try to answer the next questions.

Is the dye restored in the presence of boiled meat slurry?

Is succinic acid necessary for this reaction?

Is the behavior of enzymes from tissues similar at high temperatures?

And now - explanations. Dehydrogenases in fresh milk accelerate the formaldehyde oxidation reaction (this is seen in the discoloration of methylene blue). The blue color can be restored to the reduced dye by oxidizing it with atmospheric oxygen. Milk dehydrogenase at low temperature "works" slowly; after boiling milk, it completely loses activity. This means that this enzyme also has an optimal reaction temperature.

In experiments with muscle slurry, succinic acid dehydrogenase, like all enzymes, loses activity after boiling. In the absence of succinic acid, the reaction also does not proceed (if you washed the slurry well with water and thus removed the succinic acid contained in it). The enzyme quickly oxidizes succinic acid to fumaric acid, transferring hydrogen atoms to the dye.

And one more experiment with the same enzyme, but with another object - with microorganisms. So far, you have dealt with animal and plant tissues. However, microorganisms are perhaps even better armed with enzymes: after all, they have no other means of fighting for existence, except for biochemical ones. With one of the microorganisms, or rather, fungi, we will set up an experiment. We are talking about ordinary baker's yeast. Among the many active enzymes that are produced by yeast, there is the familiar dehydrogenase.

Rub a piece of pressed yeast on a saucer with two teaspoons of boiled water. Grind better with a plastic or aluminum spoon. When the mixture becomes homogeneous, pipette it with a clean pipette into two test tubes. They must first be washed with soap with a cotton swab on a stick, rinsed with water and dried. With another pipette, add some oil to both test tubes.

Place test tube 1 in a pot of boiling water for five minutes and cool to room temperature. Add a pinch of granulated sugar to both test tubes and shake gently to dissolve the sugar. With the third pipette, inject 10-15 drops of the dye solution into both test tubes. Observe the color of the solution.

The experiment can be somewhat complicated, for this you need more test tubes. Try changing the temperature of the solution, taking different amounts of yeast and granulated sugar. And we leave it to you to draw your own conclusions, without any leading questions. Now that you have accumulated enough experience, you are quite capable of it.

Author: Olgin O.M.

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