NOMENCLATURE OF ENZYME
Following roles are followed for the naming of enzymes:
I. All enzyme names end with the suffix ase. They are named after their substrate. For example urease acts upon urea. The sucrase acts upon sucrose.
- They may be named on the nature of the reaction that they catalyze. For example, oxidase promotes oxidation with the help of molecular oxygen. Dehydrogenase catalyses the removal of hydrogen. lsomerase catalyses the transformation of a molecule into its isomeric form.
- But several digestive enzymes were discovered earlier. They do not follow this rule. For example, pepsin and trypsin.
- Some enzymes are given a double name. One name is for the substrate and the other for the reaction that the substrate undergoes. For example alcohol dehydrogenase catalyses the dehydrogenation of ethyl alcohol and pyruvic carboxylase catalyses the removal of carbon dioxide from the carboxyl group of pyruvic acid.
CLASSIFICATION OF ENZYMES
The International Union of Biochemists set up a Commission on Enzymes. This commission divides the enzymes into six major groups on the basis of the biological reactions they catalyze. These are divided into subclasses and further subclasses. There are following six major groups of enzymes.
TheSe enzymes catalyze biological oxidations and reductions. They are further subdivided into oxidases, peroxidases, catalases, dehydrogenases and reductase. For example, nitrate reductase catalyses the reduction of nitrate into nitrite in the presence of the coenzyme NADH.
2. Transferases: These enzymes catalyze the transfer of a group from one kind of molecule to another. They are subdivided into the following subclasses according to the group transferred.
. Hyd •olases: These enzymes catalyses the hydrolysis of the mole .ales of organic foods, polysaccharides, fats and proteins. In the procesz„ the large food molecules are split into smaller fragments by
the add?. of water. Thus these enzymes are also called digestive or
hydrolytk ti.–vines. This group includes following enzymes: .
(i) Diastase- ll:ey hydrolyze starch into glucose. It occurs in germina: ng seeds, leaves and storage organs. The component enzymes of “diastase system” are amylase, maltase and dextrinases. Amylase occurs in two forms a-amylase and f3-amylase. Both these enzymes hydrolyse starch to smaller units called dextrins. Amylase hydrolyses the amylose fraction maltose.
(ii) Maltase: It hydrolyses maltose into two molecules of glucose. (iii)Sucrase: It hydrolyses sucrose (cane-sugar) into glucose and fructose.
(iv) Lipase: It hydrolyses fats into fatty acids and glycerol. It is present in oil seeds like castor bean.
(v)Phosphorylase: It catalyses the reversible splitting of
carbohydrates with the help of phosphoric acid. (vi)Phosphatase: It catalyses the removal of phosphoric acid (P) from esters of phosphoric acid.
4. Lyases or addition enzyme: The•_,tt enzymes remove or add group from or to a double bond of an otganic molecule. The names of subclasses are given on the basis of group removed or added. Its examples are hydrases (water), carboxylases (CO2) and aminases (ammonia).
lsomerases: They change organic molecule into its isomeric form. These include isomerases. epimerases and mutases:
(i) Isomerases: The:. catalyze the reversible isomerization of aldose and ketose sugars. Iheir examples are phosphotriose isomerase and phosphohe xnsc kcmierase.
(ii)Epimerases: I hey cause structural change in the molecule of a sugar or I derivative. ‘Finis two forms of molecules are formed. ‘l’lice rins are called epimers. IN example is
ph • Letopentose cpimerase.
ibey shin the position of a group within a molecule. 1 example of mutase phosphogb ceromutase.
6. Ligases: These olio :nes link two molecules along with the ‘,real:clown of a pyrophosphate bond (PP) of ATP. They are also
called synthetases. These enzymes catalyze the:
(i) Joining of amino acids to RNA molecules.
(ii) The synthesis of the amide asparagines by joining aspartic acid and ammonia.
(iii) The synthesis of fattyacyl CoA complex from fatty acids and Co-A in the synthesis of fats.
(iv) The joining of amino acids by peptide bonds to form polypeptides
(v) The synthesis of citric acid by the linking of the acetyl group of acetyl-CoA to oxaloacetic acid.