enzymes classification of enzyme and -isoenzymes-1

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Assignment

Name Amjad Khan Submitted to Dear Sir Ghadir Ali Subject Bacterial Phasology and Anatomy Topic ENZYMES & CLASSIFICATION OF

ENZYMES Date 06/06/2015

ENZYMES

Definition Enzymes are protein catalysts for

biochemical reactions in living cells

They are among the most remarkable biomolecules known because of their extraordinary specificity and catalytic power, which are far greater than those of man-made catalysts.

Naming

The name enzyme (from Greek word "in yeast")was not used until 1877, but much earlier it was suspected that biological catalysts are involved in the fermentation of sugar to form alcohol (hence the earlier name "ferments").

Naming and Classification of Enzymes

Many enzymes have been named by adding the suffix -ase to the name of the substrate, i.e., the molecule on which the enzyme exerts catalytic action.

For example, urease catalyzes hydrolysis of urea to ammonia and CO2, arginase catalyzes the hydrolysis of arginine to ornithine and urea, and phosphatase the hydrolysis of phosphate esters.

Classification of enzymes Oxido-reductases (oxidation-

reduction reaction). Transferases (transfer of functional

groups). Hydrolases (hydrolysis reaction). Lyases (addition to double bonds). Isomerases (izomerization

reactions). Ligases (formation of bonds with ATP

cleavage).

The structure of enzymes Protein part + Non- protein part Apoenzyme + Cofactor = Holoenzyme

Function of apoenzyme: It is responsible for the reaction Function of cofactor: It is responsible for the bonds formation

between enzyme and substrate Transfer of functional groups Takes plase in the formation of tertiary

structure of protein part

Cofactor

1. Prosthetic group (when cofactor is very tightly bound to the apoenzyme and has small size )

2. Metal ion 3. Coenzyme(organic molecule

derived from the B vitamin which participate directly in enzymatic reactions)

Prosthetic group

1. Heme group of cytochromes

2. Biothin group of acetyl-CoA carboxylase

Metal ions Fe - cytochrome oxidase, catalase Cu - cytochrome oxidase, catalase Zn - alcohol dehydrogenase Mg - hexokinase, glucose-6-

phosphatase K, Mg - pyruvate kinase Na, K – ATP-ase

Coenzyme B1 TPP- Thiamine Pyro Phosphate B2 FAD- Flavin Adenine Dinucleotide FMN- Flavin Mono Nucleotide Pantothenic acid Coenzyme A (CoA) B5 NAD – Nicotinamide Adenine

Dinucleotide NADP- Nicotinamide Adenine

Dinucleotide Phosphate

Chemical Kinetics

The Michaelis-Menten Equation

In 1913 a general theory of enzyme action and kinetics was developed by Leonor Michaelis and Maud Menten.

1. Point А.

2. Point В.

3. Point С.

Mechanism of enzyme reaction 1. Formation of enzyme – substrate

complex E + S → ES 2. Conversion of the substrate to

the product ES→ EP 3. Release of the product from the

enzyme EP → E+P

The Free Energy of Activation Before a chemical reaction can

take place, the reactants must become activated.

This needs a certain amount of energy which is termed the energy of activation.

It is defined as the minimum amount of energy which is required of a molecule to take part in a reaction.

The Free Energy of Activation For example,decomposition of

hydrogen peroxide without a catalyst has an energy activation about 18 000. When the enzyme catalase is added, it is less than 2000.

The Free Energy of Activation The rate of the reaction is

proportional to the energy of activation:

Greater the energy of activation Slower will be the reaction While if the energy of activation is

less, The reaction will be faster

Energy of Activation

Effect of pH on Enzymatic Activity

Most enzymes have a characteristic pH at which their activity is maximal (pH- optimum);

above or below this pH the activity declines. Although the pH-activity profiles of many enzymes are bell-shaped, they may be very considerably in form.

Effect of pH on Enzymatic Activity

Effect of Temperature on Enzymatic Reactions

.The rate of enzyme catalysed reaction generally increases with temperature range in which the enzyme is stable. The rate of most enzymatic reactions doubles for each 100 C rise in temperature. This is true only up to about 500 C. Above this temperature, we observe heat inactivation of enzymes.

The optimum temperature of an enzyme is that temperature at which the greatest amount of substrate is changed in unit time.

Effect of Temperature on Enzymatic Reactions

1. Reversible inhibitionA. Competitive

B. Non-competitive C. Uncompetitive

2. Irreversible inhibition

Competitive Inhibition

Usage competitive inhibition in medicine The antibacterial effects of

sulfanilamides are also explained by their close resemblance to para-amino-benzoic acid which is a part of folic acid, an essential normal constituent of bacterial cells. The sulfanilamides inhibit the formation of folic acid by bacterial cells and thus the bacterial multiplication is prevented and they soon die.

Non-competitive Inhibition In this case, there is no structural

resemblance between the inhibitor and the substrate. The inhibitor does not combine with the enzyme at its active site but combines at some other site.

E + S +I =ESI (INACTIVE COMPLEX)E + S = ESES + I = ESI

Uncompetitive inhibition

E + S +I =ESI (No active complex)

Irreversible Inhibition The inhibitor is covalently linked to

the enzyme. The example: Action of nerve gas poisons on

acetylcholinesterase,an enzyme that has an important role in the transmission of nerve impulse.

Isoenzymes

Lactate dehydrogenase It occurs in 5 possible forms in the

blood serum: LDH1

LDH2

LDH3

LDH4

LDH5

Structure of LDH Each contains 4 polypeptide chains

which are of 2 types: A and B which are usually called M (muscle) and H (heart).

LDH1 –H H H H LDH2 – H H H M LDH3 – H H M M LDH4 – H M M M LDH5 – M M M M

Clinical importance of LDH Acute myocardial infarction LDH1 and LDH2 Acute liver damage LDH4 and LDH5

Creatine kinase It has 3 isoenzymes: CK1

CK2

CK3

Clinical importance: When patient have acute myocardial

infarction CK appears in the blood 4 to 8 hours after onset of infarction and reaches a peak in activity after 24 hours.

Enzyme-Activity Units

The most widely used unit of enzyme activity is international unit defined as that amount which causes transformation of 1.0 mkmol of substrate per minute at 25°C under

The specific activity is the number of enzyme units per milligram of protein.

Enzyme-Activity Units

The molar or molecular activity, is the number of substrate molecules transformed per minute by a single enzyme molecule

The katal (abbreviated kat),

defined as the amount of enzyme that transforms 1 mol of substrate per 1 sec.

THE END

Thank you 06/06/2015