Properties of Enzymes, Co-factor and Enzyme Action


The catalytic activity of an enzyme is due to active site. It is a small portion of enzyme consisting of few amino acids.

The enzyme and its substrate react with each other through active sites.

The active site is a three dimensional cavity bearing a specific charge.

Most of the enzymes have a non-protein part known as a co-factor.

Cofactor is directly involved in chemical reaction for catalysis. Cofactor acts as “bridge”between enzyme and its substrate. Sometimes the co-factor provides energy to drive the reactions.

There are three kinds of a cofactor:

  1. The detachable inorganic ion (metal ion) working as co-factor is known as an activator. e.g., Cu/Zn.
  2. The covalently bonded non-protein part of enzymes is known as prosthetic group. e.g., Lipids.
  3. If the non- protein portion is loosely attached to the protein part it is known as coenzyme. e.g., Vitamins.

An enzyme with its coenzyme or prosthetic group removed is called Apoenzyme.

An activated enzyme consisting of polypeptide chain and a cofactor is known as Holoenzyme.

The conditions under which enzymatic activity is destroyed by disrupting bonds between the atoms in an enzyme are: High temperature and extreme changes in pH.

Enzymes are also produced in the cells near the site of function.

Many enzymes are dissolved in the cytoplasm. Others are bound to the subcellular organelles. For example:

  1. Enzymes for photosynthesis are present in the Chloroplasts.
  2. Enzymes for cellular respiration are present in the Mitochondria.
  3. Some enzymes of protein synthesis are present in Ribosomes.

All metabolic activities occurring in the cells are carried out by specific enzymes.

Enzymes are sensitive to a small change in pH, temperature and substrate concentration.

Some enzymes are damaging if they become active in the wrong place. Pepsin is produced in inactive pepsinogen form. If it is produced in the active form it may cause cancer.

Mechanism of enzyme action is called catalysis.

The active site of the enzyme is made up of binding site and catalytic site.

The binding site helps in identification/Recognition and binding of a proper Substrate to form E-S complex. This reaction activates the catalytic site. The catalytic site catalyzes the transformation of substrate into product(s). The enzyme after catalysis detaches fromthe product unchanged

An enzyme has specific function because its chemistry and configuration (shape) is specific. Any factor that can change the chemistry and shape of an enzyme can affect its rate of catalysis.

Some factors that can affect the rate of enzyme action are: enzyme concentration, substrate concentration, temperature, and pH value.

If substrate concentration is unlimited then the rate of reaction depends on the amount of enzyme present at a specific time. If the amount of enzyme is doubled the reaction rate is also doubled.

Reason: The increase in enzyme number causes increase in active sites. More active sites will convert more substrate into product(s), in a given time.

At low substrate concentration the reaction rate is directly proportional to the substrate.

If the enzyme concentration is constant, the rate of reaction increases with an increase with substrate concentration.

The temperature at which activity of enzyme is maximum is called as optimum temperature. The increase in temperature causes increase in reaction rate of enzyme up to a certain limit. For enzymes of human body 37oC is the optimum temperature.

Heat provides activationenergy. Heat also supplies kineticenergy to the molecules. At high temperature globular structure is lost and the enzyme is denatured. Globular structure is necessary for enzyme activity.

The enzymes function at narrow pH range is called optimum pH. A slight change in pH can change the ionization of the amino acids at the active site and the ionization of the substrates. Now enzyme activity is either retard or blocked completely. A great change in pH causes the bonds in the enzyme to break. The result is the denaturation of enzyme.

A condition in which all of the active sites of enzymes are occupied by substrate molecules is called Enzyme saturation.

A complex consisting of an enzyme and its reactant (substrate) which is held together by weak bonds is called Enzyme-substrate (ES) complex. The formation of an ES is the first step in enzyme catalysis.

A type of metabolic pathway control that regulates the rate at which the cells synthesize amino acids (or other monomers) and use them in building proteins (or other polymers) is called Feedback inhibition.

An organic molecule that functions as a coenzyme is the Vitamin.

Allosteric enzyme is an enzyme that undergoes reversible changes in shape and in catalytic activity.


Enzyme Function pH Value
Arginase Catalysis of arginine into urea 9.70
Catalase Decomposition of hydrogen peroxide 7.60
Chymotrypsin Involved in proteolysis 7.00-8.00
Enterokinase Activation of trypsinogen 5.50
Pancreatic lipase Hydrolysis of fats 9.00
Pepsin Digestion of proteins 2.00
Salivary amylase Digestion of carbohydrate 6.80
Sucrase Hydrolysis of sucrose 4.50