Chemistry Of Enzyme

Enzyme:

Enzyme are the macromolecular protein biocatalyst.It speed up the chemical reactions without being changed in overall process.Enzymes are the central part of every biochemical process.The study of enzyme is called Enzymology.
The enzyme can catalyze more than 5000 types of biochemical reactions. 

History Of Enzyme:  

The biological catalyst was first time recognized in late 1700s during study on digestion of meat in stomach through some Chemical secretions.In 1850s,Louis posture concluded the experiment of fermentation in which sugar molecules is converted into alcohol by the help of yeast ferments.In 1877,FREDERICH WILHELM KUHNE called these yeast ferment molecule "ENZYME"

Later,enzyme used for non living substances such as pepsin and the ferment used for the chemical activity that is produced by living organisms.

Classification Of Enzyme:

Enzymes are classified into six major classes:

1. Oxidoreductase:

          Oxidoreductase are those enzyme Which catalyze oxidation- reduction reactions,such as:

2.  Transferases:

           Transferases are those enzyme which help in transfer of functional group (amino group or phosphate group)such as

3.  Hydrolases:

        Hydrolases are those enzyme which help in transfer of water because they catalyze hydrolysis of substrate,such as:

4.  Lyases:

         Lyases are those enzyme which helps in addition or removal of water,ammonia,carbon dioxide to form a double bond Such as:

5.  Isomerases:

          Isomerases are those enzyme which catalyze rearrangement of atoms within a molecule,such as:

6.  Ligases:

           ligases are those enzyme which helps in joining of 2 molecules,suchvas:

Structure Of Enzyme:

Enzymes are globular proteins.Like proteins,it consist of linear chains of aminoacids that fold together to form a 3D structure.The catalytic activity of enzyme is depend upon the specific sequence of aminoacids.Enzymes are much larger than their substrate.It contains active site and allosteric site.Active site for binding of substrate and allosteric site for binding of a small molecule which causes confirmational changes in enzyme structure that increase or decrease enzyme activity.

Properties Of Enzyme:

Basically Enzymes are protein biocatalyst that increase the velocity of chemical reaction without being consumed during the reaction.It do not alters the equilibrium of reaction.

1.  Active site:

Enzyme molecule contains a specific cleft called active site.It is formed by the folding of proteins that contains aminoacid side chain that helps in the binding of substrate and catalyses.substrate binds with enzyme formed enzyme-substrate(ES)complex which causes confirmational changes in enzyme and allow catalysis.Then ES converted into an enzyme-product(EP)complex which dissociate into enzyme and product.

2.  Catalytic Efficiency:

Enzyme-catalyzed reactions are highly efficient.It increase the rate of reaction by lowering its A.E.

3.  Specificity:

Enzyme are highly specific in nature due to its 3D structure.It interacts with one or few substrates and catalyzed only one type of chemical reaction.

4. Holoenzyme:

Enzyme with its non-protein component is called holoenzyme.It is active in natue.

5. Apoenzyme:

The enzyme without its non-protein component is called apoenzyme.It is inactive in nature.

6. Cofactor:

In enzyme if non-protein component is a metal ion such as Zinc ion or ferrous ion is called cofactor.

7.  Co-Enzyme:

If non protein component is a small organic molecule in enzyme is called co-enzyme.It is commonly derived from vitamins.For example NAD+ contains niacin,FAD contains riboflavin.

8.  Regulation:

The activity of enzyme is regulated either by increased or decreased rate of product formation depending upon need of cell.

9.  Ribozyme:

Some RNA act like enzymes called ribozymes which catalyzed cleavage and synthesis of phosphodiester bond.

Mechanism Of Enzyme:

As we know that enzymes are very imp b/c it mediates all chemical reactions of life.It is highly specific for particular reactions.Enzyme perform their work by following ways:

1.  Substrate Binding:

Enzymes are highly specific in nature so it bind with specific substrate to catalyze any chemical reaction.

2. Energy Changes:

During chemical reaction,when enzyme bind with substrate some energy changes occur.Enzyme overcomes a barrier of energy called A.E and convert the reactant A into product B through the transition state.

3.  Rate Of Reaction:

In the presence of enzyme,more molecules have sufficient amount of energy to overcome a energy barrier of transition state.By this way it fasters the rate of reaction by lowering its energy of activation.

Theories Of Enzyme:

1. Key And Lock Theory:

In 1894, EMIL FISHER proposed that," Both enzyme and substrate possess specific complementary geometric shape that fit exactly into one another.He called it lock and key model.This theory explains enzyme specificity but fails to explain the enzyme stability.

2.  Induced Fit Model Theory:

In 1958, DANIEL KOSHLAND proposed induced fit model.He explained that," when a substrate bind with enzyme induce changes in enzyme structure and these changes enable enzyme to perform its catalytic activity more effectively.

Factors Affecting Enzyme Activity:

Following are the factors which affect the enzyme activity:

1. Substrate Concentration:

The rate of reaction increases with an increase of concentration of substrate.At very high concentration of substrate,enzyme exert retarding effect on enzyme activity.

2. Effect Of Temperature:

Enzymes are sensitive to temperature.Every enzyme has its own temperature and below this temperature enzyme activity is decreased.Enzymes are highly active at 37°C and destroyed at 100°C .At 0°C its activity is reduced to minimum but not destroyed.

3. Effect Of pH:

The activity of enzyme vary with change of pH.Generally each enzyme has its own optimum pH.Extreme of pH can also lead to denaturation of enzyme.For e.g: pepsin has optimum pH 2.It is inactive in neutral or alkaline solution.

4. Inhibitor:

Inhibitor are those substances which decrease the activity of enzyme.It directly combine with enzyme or may act with activator so activator is not available for activation of enzyme.

Types Of Inhibitor:

1. Competitive Inhibitors:

competitive inhibitors are resemble with the real substrate of enzyme.It binds with active site of an enzyme by blocking the substrate.This type of inhibition can be overcome with high substrate concentration.

2. Non-Competitive Inhibitors:

Non-competitive inhibitors binds with an allosteric site of enzyme and obstruct the enzymatic activity and substrate still binds with active site of enzyme with usual affinity.It is not overcome with high substrate concentration.

Biological Functions Of Enzyme:

Enzyme performs several functions in living organism:

1. They help in signal transduction and cell regulation by kinases and phosphatases.
2. In cell membrane,ATPase enzyme are present that act as an ion pump,involved in active transport.
3. In animals, it helps in the digestion of food such as proteases and amylases which convert the larger molecules into smaller molecules so they can be easily absorbed by intestine.
4. some viruses also contain enzymes for causing infection in cells such as influenza virus has nuraminidase.etc.