Classification Of Enzymes

                                                             Blog by - Mr. Navnath Pawar

Classification Of Enzymes -

          Enzymes are biocatalysts that are proteinaceous (and even nucleic acids) and change the rate of a reaction. Thousands of chemical reactions take place at any given time in all of an organism's live cells. Enzymes, which are wonderful molecular machines, mediate nearly all of these processes. Enzymes are the catalysts of biological systems because they are at the heart of every metabolic reaction (biocatalysts). They catalyze hundreds of sequential reactions that degrade food molecules, store and transform chemical energy, and produce biological macromolecules from simple substrates in structured sequences. Metabolic pathways are closely coordinated through the action of regulatory enzymes, resulting in a harmonious balance among the many distinct activities required to sustain life.      Enzymes catalyze an unlimited diversity of biochemical reactions because of their capacity to specifically bind a awfully wide selection of molecules. By utilizing the complete repertoire of intermolecular forces, enzymes bring substrates together in an optimal orientation, the prelude to creating and breaking chemical bonds.

    They catalyze reactions by stabilizing transition states, the best energy-species in reaction pathways. By selectively stabilizing a transition state, an enzyme determines which one amongst several potential biochemical reactions actually takes place.

    All enzymes are protein but all protein aren't enzymes, initially at the time of origin RNA play role as a enzyme e.g. ribozymes. Until 1980s, all enzymes were believed to be proteins. Then, Tom Cech and Sidney Altman independently discovered that certain RNA molecules may function as enzymes is also effective biocatalysts. These RNA biocatalysts have come to be called ribozymes.

Enzymes are broadly divided into six groups based on the type of reaction catalyzed.

They are:

(1) Oxidoreductases

(2) Transferases

(3) Hydrolases                                               ( O T H L I L )

(4) Lyases

(5) Isomerases and

(6) Ligases.

 

(a) Oxidoreductases:

          Enzymes which bring about oxidation and reduction reactions.

Ex. Pyruvate + NADH—lactate dehydrogenase → Lactate + NAD ⁺

Glutamic acid + NAD—glutamate dehydrogenase → α-ketoglutarate + NH₃ + NADH

(b) Transferases:

          Enzymes which catalyze transfer of groups from one substrate to another, other than hydrogen. Ex. Transaminase catalyzes transfer of amino group from amino acid to a keto acid to form a new keto acid and a new amino acid.

Ex. (α-Ketoglutarate + Alanine—alanine aminotransferase → Glutamate + Pyruvate

Aspartate + α-Ketoglutarate —aspartate aminotransferase Oxaloacetate + Glutamate

 

 

 

(c) Hydrolases:

          Those enzymes which catalyze the breakage of bonds with addition of water (hydrolysis). All the digestive enzymes are hydrolases. Ex. Pepsin, trypsin, amylase, maltase.

(d) Lyases:

          Those enzymes which catalyze the breakage of a compound into two substances by mechanism other than addition of water. The resulting product always has a double bond.

Ex. Fructose-1-6-diphosphate—ALDOLASE → Glyceraldehyde-3-phosphate + DHAP

(e) Isomerases:

          Those enzymes which catalyze the inter-conversion of optical and geometric isomers.

Ex. Glyceraldehyde-3-phosphate—ISOMERASE → Dihydroxyacetone phosphate

(f) Ligases:

          These enzymes catalyze union of two compounds. This is always an energy requiring process (active process).

Ex. Pyruvate + CO₂ + ATP—pyruvate carboxylase Oxaloacetate + ADP + Pi.