1. Lab Activity 10 Enzymes
IUG, 2015
Dr. Tarek Zaida

2. Background
An enzyme is a protein molecule that is a biological catalyst with three characteristics:
First, the basic function of an enzyme is to increase the rate of a reaction. Most cellular reactions occur about a million times faster than they would in the absence of an enzyme.
Second, most enzymes act specifically with only one reactant (called a substrate) to produce products.
Third and most remarkable characteristic is that enzymes are regulated from a state of low activity to high activity and vice versa.

3. IEC Classification of Enzymes Type of Reaction catalyzed
Classes of Enzymes
IEC Classification of Enzymes
Group Name
Type of Reaction catalyzed
Oxidases or Dehydrogenases
Oxidation-reduction reactions
 Transferases
Transfer of functional groups
 Hydrolases
Hydrolysis reactions
Lyases
Addition to double bonds or its reverse
Isomerases
Isomerization reactions
Ligases or Synthetases
Formation of bonds with ATP cleavage

4. Comparative Activity of Enzymes and Nonbiological Catalysts
Enzymes are different from other nonbiological catalysts (metals, acids, and salts) in the fact that they exhibit a high catalytic efficiency, specificity of action, and ability to accelerate reactions under mild conditions.

5. 1% solution of Starch in 0.3% aqueous NaCl solution
Experiment 1 Comparison of Action Exerted by Salivary α-Amylase and Hydrochloric Acid on Starch Hydrolysis Reaction
Reagents & Materials
1% solution of Starch in 0.3% aqueous NaCl solution
Iodinated potassium iodide solution,
Benedict’s solution.
Test tube stand with a set of test tubes, a funnel, glass rod, eye pipettes, a thermometer, pipettes of 5 ml capacity.

6. Preparation of dilute Saliva
Rinse your mouth thoroughly to remove eventually food remnants.
Take a portion of distilled water (about 20 ml) in your mouth and keep it in for about 2 min. to allow it to mix the salivary secretion; use your tongue as a stirrer. Let the salivary liquid out into a beaker
Pour the contents into a funnel with a cotton wad in it for a filter and filter off the liquid.
Set aside the filtrate to be used in further exp.

7. Procedure
Transfer 1 ml of distilled water to a test tube, 1 ml of hydrochloric acid solution to another test tube, 1 ml of dilute saliva to a third test tube.
Add 5 ml of starch solution to each of the three test tubes, stir the contents with a glass rod.
Place the first and the third test tubes in a water bath at 38 C, and the second test tube in a boiling water bath.

8. 4. In 15 min let the test tubes cool. 5
4. In 15 min let the test tubes cool. 5. Sample 5 drops from each test tube into three clean test tubes. 6. Add 1-2 drops of iodine solution and compare the coloration developed in the samples. 7 . To test for maltose sample 3 ml from each test tube, add 1 ml of Benedict’s solution and heat the upper layer of the mixture to boiling. 8. Note the formation of a red cuprous oxide precipitate in the samples.

9. Experiment 2 Identification of Enzymes of Different Groups
Identification of Oxidoreductases in Biological Material
Identification of Aldehyde Oxidase (Aldehyde: Oxygen Oxidoreductase; EC ) in milk

10. Identification of Oxidoreductases in Biological Material
For most enzymes of this group, the recommended names are dehydrogenases and reductases.
When O2 is the acceptor, the term oxidase is used;
If the oxygen is involved in the reaction, makes part of the substrate, the enzyme is named oxygenase.
Peroxidase is an enzyme that utilizes H2O2 as an acceptor, and catalase is an enzyme capable of catalyzing the reaction in which a donor-acceptor pair is involved, which is composed of 2 H2O2 molecules

11. Reagents & Materials
0.4% aqueous solution of Formaldehyde,
0.01% aqueous solution of Methylene Blue
Test tube stand with test tubes
Water bath
Thermometer
Pipettes of 1 and 5 ml capacity.

12. Identification of Aldehyde Oxidase (Aldehyde: Oxygen Oxidoreductase; EC1.2.3.1) in milk
The method is based on visual observation of Methylene Blue (MB) decoloration by binding the hydrogen abstracted from the substrate through the aid of aldehyde oxidase
Aldehyde Oxidase is a catalyst for the dehydrogenation reaction of a variety of aldehydes, for example formaldehyde.
Hydrogen is transferred onto FAD which is a coenzyme for the given enzyme, and then onto the final acceptor (oxygen) according to the scheme.

13. H2C=O + H2O + FAD HCOOH + FADH2 FADH2 + O2 FAD + H2O2
MB as a model hydrogen acceptor, on its addition to the system studied, is converted to a reduced form (leucoform), MBH2:
H2C=O H2O + MB HCOOH +MBH2
The colorless methylene Blue solution on vigorous shaking regains the initial blue color.
MBH2 + O MB + H2O2
Aldehyde oxidase
Aldehyde oxidase
Aldehyde oxidase
FAD
FADH2

14. Procedure
Transfer 5 ml of fresh milk to 2 test tubes
Add 2 ml of distilled water to one test tube and an equal volume of formaldehyde solution to the other test tube.
Pour 0.5 ml of Methylene Blue into each test tube, mix the contents with shaking and add 3 to 4 drops of vaseline oil (or paraffin oil) to prevent contact of liquid mixture with ambient oxygen.

15. 4. Place the test tubes in a water bath at 37C
4. Place the test tubes in a water bath at 37C. Within 10 – 15 min note a change in sample color. Shake vigorously the test tubes and observe again a change in color.