ENZYMES

ENZYMES Are chemical substance which hastens chemical

reaction without being affected in the process.

Are secreted by living cells, and are complex organic chemical compounds with definite structure.

Like the inorganic catalysts, enzymes have the remarkable property of speeding up chemical reactions without being themselves affected in the process. As a result they can be use over and over again.

Catalysts or enzymes are responsible for different biological changes.

They make up the largest and most highly specialized class of proteins.

The catalytic efficiency of enzyme is so high that per mole is around 10,000 to 10,000,000 moles of substrate per minute.

The catalytic action of enzymes is the key to their importance, for by facilitating chemical changes, enzymes make possible the continuous replacement and renewal processes of all living organisms.

NOMENCLATURE With the increasing number of known enzymes, it

is essential that a more systematic nomenclature be adopted. Therefore, enzymes are now designated by the suffix ase proceed by the term which indicates the following:

1. General nature of the substrate ex. Lipase-acting upon liquid.

2. Actual name of the subsrate ex. Sucrase- acting on sucrose.

3. Type of reaction catalyzed ex. Oxidase-catalyzes oxidation.

4. Combination of several of these designation ex. Xanthine oxidase-catalyzes oxydation of xanthine.

In case of the hydrolytic enzymes, the suffix adjective lytic is used.

amylolytic, lipolytic, proteolytic enzymes The inactive form of enzyme is the pro-enzyme

or zymogen. The suffix ogen is affixed to the name of the active enzyme.

pestrinogen, trypsinogen, reninogen-they exhibit the property of true enzyme only after they are activated by suitable hydrogen ion concentration or by an organic activator called kinase.

CLASSIFICATION

1. Oxido-reductases (cause oxidation reduction reaction)

1.1– acts on –CH-OH (secondary alcohol)

1.2- acts on -C=O (ketone)1.3- acts on –CH=C- (alkene)1.4- acts on -CH-NH2 (primary amine1.5- acts on -CH-NH- (secondary

amine)1.6- acts on NADH3 NADPH

2. Transferases (transfer functional group)

2.1- one carbon group2.2- aldehyde or ketonic group2.3- acyl group2.4- glycerol groups2.5- phosphate group2.6- S-containing group

3. Hydrolases (causes hydrolysis)

3.1- esters3.2- glycosidic bonds3.3- peptide bonds3.4- other C-N bonds3.5- acyl anhydrides

4. Lyases (addition of double bonds)

4.1- C=C (alkene)4.2 C=O (ketone)4.3 C=N (cyanide)

5. Isomerases (isomerization reaction)

5.1- Racemases

6. Ligases (formation of bonds with ATP cleavage)

6.1- C-O6.2- C-S6.3- C-N6.4- C-C

FUNCTIONS OF ENZYMES

Enzymes are indispensable for signal transduction and cell regulation, often via kinases and phosphatases.

Generate movement, with myosin hydrolyzing ATP to generate muscle contraction and also moving cargo around the cell as part of the cytoskeleton.

Enzymes are also involved in more exotic functions, such as luciferase generating light in fireflies.

Viruses can also contain enzymes for infecting cells, such as the HIV integrase and reverse transcriptase, or for viral release from cells, like the influenza virus neuraminidase.

An important function of enzymes is in the digestive systems of animals. Enzymes such as amylases and proteases break down large molecules (starch or proteins, respectively) into smaller ones, so they can be absorbed by the intestines. Starch molecules, for example, are too large to be absorbed from the intestine, but enzymes hydrolyze the starch chains into smaller molecules such as maltose and eventually glucose, which can then be absorbed. Different enzymes digest different food substances.

FACTORS AFFECTING THE RATE OF ENZYME ACTION:

1. Concentration of Enzyme and its substrate: other conditions being constant, the rate of reaction depends on the concentration of enzyme and substrate.

2. The effect of Temperature: on enzyme reaction is two. A region high temperature in which the rate decreases with increased temperature due to the thermal inactivation of the enzyme (denaturation). Optimum temperature 37˚C-40˚C

3. Effect of pH: most enzymes have a characteristic pH at which the activity is maximal. The pH activity profiles of enzymes are not always shaped. They may even be rectilinear.

4. The effect of Time: Time is important element in defining other conditions which regulate the rate of enzyme motion.

5. The products of Reaction: the rate enzyme action decreases on the product of reaction increases. This is due to the reversibility off enzyme action.

Sucrase Sucrose Glucose + Fructose

6. Light and other physical agents: light rays affect the activity of enzymes. Blue and red lights increases the activity of salivary amylase, while ultraviolet rays and radium exert inhibitory effect. Violet shaking destroys the enzymes by causing denaturation.

7.Chemical agents: some chemical agents accelerate enzyme action. Ex. If salivary amylase is (freed from sodium chloride) it becomes inactive.

PROPERTIES OF ENZYMES

1. Molecule composed from one or more protein chains2. Catalytic action; elevated catalytic power3. Reduction of activation energy4. Elevated specificity5. Active site6. Inhibition by specific molecules

Structure and Function of an Enzyme

Enzymes are large proteins that speed up chemical reactions. In their globular structure, one or more polypeptide chains twist and fold, bringing together a small number of amino acids to form the active site, or the location on the enzyme where the substrate binds and the reaction takes place. Enzyme and substrate fail to bind if their shapes do not fit each other. This ensures that the enzyme does not participate in the wrong reaction. The enzyme itself is unaffected by the reaction. When the products have been released, the enzyme is ready to bind with a new substrate.

CLINICAL APPLICATION OF ENZYMES*Medical and clinical uses of enzymes:1. Drugs for digestive disorders -Some digestive enzymes such as amylases are often used as s components of drugs to cure digestive disorders.

2. Deworming medicines -The plant proteases like ‘papain’ (from papaya) and ‘ficin’ (from fig) lire used as deworming medicines for humans and domestic animals.

These enzymes are not inhibited by the secretions of the worms and cause digestion of the worms.

3. Enzymes to stop bleeding -The enzyme ‘thrombin’ obtained from beef plasma is used topically to stop bleeding during operations and after tooth extraction. The enzyme converts fibrinogen to fibrin and small peptides, which are then insolubilized causing blood to clot.

4. Enzymes as surface disinfectants -‘Trypsin’ has been used in cleaning away thick, purulent (full of pus) masses in surface infections and in emphysema (enlargement of vesicles of lungs) associated with pleural pneumonia. The area cleaned by its digestive action heals much more rapidly than untreated area. The two other enzymes ‘ficin’ and ‘streptodornase’ are also used sometimes as wound debridement.

5. Diagnosis of diabetes -‘Glucose oxidase’ in combination with ‘peroxidase’ is used for colorimetric determination of glucose in blood. This test generally conducted to determine the level of blood sugar thus leading to diagnosis of diabetes.

ENZYMES AND RELATED DISEASES Acid Phosphatase- some prostatic disease Alanine aminotransferase (ALT)- Liver, Heart

diseases Aldolase- some muscle diseases Alkaline Phosphate- Liver and Bone diseses Amylase- pancreatic diseases Angiotensin- Converting enzyme (ACE)- Active

sarcoidosis Aspartate aminotransferase (AST)- Heart, Liver

diseases

Cholinesterase (psuedocholinesterase)-acute organophosphorus poisoning

Creatine Kibase (CK or CPK)- Heart, Muscle disease

Gamma-Glutamytransferase (GGT)- Liver disease, alcohol rehabilitation

LactateDehydrogenerase (LDH)- Heart, Liver, Brain disease

Lipase- Pancreatitis Lysozymes- some acute luekemias