Enzymes Part II: Comparison of enzymes and catalysts, nomenclature and biological significance

In this article you will find the comparison of enzymes and catalysts. You will also find nomenclature of enzymes, classification of enzymes and biological significance of enzymes. To know detail of enzymes, please read this article.


you have read general introduction of enzymes, physical properties, chemical properties, general properties, chemical nature of enzymes and differences between apoenzymes and co-factor in enzymes part I . In this article you will read about the following:

  • Comparison of enzymes and catalysts
  • Nomenclature of enzymes
  • Classification of enzymes
  • Differences between enzymes and hormones
  • Biological significance of enzymes

Comparison of enzymes to catalysts

Enzymes are the bio-catalysts found in the living cells. Following similarities and dissimilarities are found in enzymes and catalysts :

Similarities between enzymes and catalysts

The similarities between enzymes and catalysts are:

  • Enzymes and inorganic catalysts both of them remain unchanged at the end of the reaction chemically and quantitatively and can be used again to catalyze another reaction.
  • Both are required in small quantities.
  • Both of them do not alter the equilibrium of the reversible reaction.
  • Both of them increase the rate of reaction by lowering the activation energy but they do not initiate the reaction.
  • The complexes formed with the reactants by both of them are short lived.

Differences between enzymes and inorganic catalysts

The differences between enzymes and catalysts are :

  • Enzymes are proteins with complex three dimensional organization whereas catalysts are small molecules or simple mineral ions.
  • Enzymes catalyze only specific biological reactions of a single or a few substrates whereas catalysts can catalyze diverse reactions.
  • Enzymes can be regulated by specific molecules which can change their conformation and activity whereas catalysts are not regulated by any regulator molecules.
  • Enzymes are more s3ensitive to changes in temperature and pH whereas catalysts are less sensitive to changes in temperature and pH.

Nomenclature of Enzymes

Different systems of nomenclature of enzymes have been proposed. Some of the systems are as follows;

Nomenclature based on the substrate

Every enzyme acts on specific substrate. According to this system enzymes are named by adding the suffix-ase after the name of the substrate. For example

  • Proteinase acts on protein molecules.
  • Maltase acts on maltose.
  • Sucrase acts on sucrose.

Nomenclature based on reaction

In this system, the enzyme is named by adding the suffix-ase at the end of reaction catalyzed by the enzyme. For example;

  • Hydrolases take part in hydrolyssis reaction.
  • Isomerases take part in isomerization reaction.
  • Dehydrogenases take part in dehydrogenation reaction.
  • Oxidases take part in oxidation reaction.

Nomenclature based on both substrate and the type of reaction

In this system, both the name of the substrate and type of reaction are used for naming the enzyme. For example:

  • Succinic acid dehydrogenase catalyses the deydrogenation of succinic acid.
  • Hexo-isomerase catalyses the conversion of one hexose sugar into other.

Nomenclature based on the source of enzyme

Some enzymes have been named according the their source of production. For example:

  • Papsin is obtianed from papaya.
  • Bromeain is obtained from pineapple.

Classification of enzymes

The system of classification has been worked out by the International Union of Biochemists and known as IUB system of the nomenclature of enzymes. In this system, classification is based on the reaction and specificity of of enzymes. According to this system all enzymes are grouped into six classes. Each class is subdivided again into sub classes.

Class-I. Oxidoreductases or Oxidases

This class includes enzymes which are concerned with biological oxidation and reduction by removing or adding electrons from the substrate. it includes following sub-classes:

  • Dehydrogenase : Catalyses the removal of hydrogen from a subtrate.
  • Oxidase: Oxidizes a molecule by adding oxygen.
  • Oxidative deaminase: Catalyzes oxidation f amino acids.

Class-II. Transferases

Transferases enzymes catalyze the transfer of a group from one substrate to another. The chemical group transferred is not in a free state. The group may be alkyl, glycosyl, amino, aldehyde, sulphur, etc. Transferases are divided into following sub-classes:

  • Transaminases : Responsible for the transfer of amino and keto group.
  • Transphosphatase : Responsible for the transfer of phosphate group.

Class-III. Hydrolases

Hydropases enzymes breakdown large molecules into smaller ones by the introduction of water and breaking of specific covalent bonds. Most of the digestive enzymes belong to this category. It can further be divided into following sub-classes:

  • Proteases or Proteolytic enzymes ; Responsible for hydrolysis of protien into peptones and peptides.
  • Carbohydrases or Amylolytic enzymes : Responsible for hydrolysis of carbohydrates.
  • Esterases or Lipolytic enzymes : Act upon lipids and break them into fatty acid and glycerol.

Class-IV. Lyases

Lyases enzymes act on C-C, C-O, C-N, C-S and O-X bonds. This results in breaking of larger substrates into smaller substrates without the addition of water.

Class-V. isomerases

Isomerases enzymes catalyze the rearrangements of molecular structure to form isomers.

Class-VI. Lygases or Synthetases

Ligases enzymes catalyze covalent bonding of two substances to form a large molecule. The energy for the reaction is derived by the hydrolysis of ATP.

Differences between Enzymes and Hormones

The differences between enzymes and hormones are as follows:

  1. Larger part of enzyme molecules consist of proteins whereas hormones may be made up of proteins, amino acids, steroids or phenolic compounds.
  2. Enzymes may be intracellular or intercellular in function wherease hormones are totally intercellular in function.
  3. Enzymes are not transported fromon organ to other whereas hormones are transported from one part to other part of the body.
  4. Enzymes are involved in the catalysis of biochemical reactions whereas hormones initiate biochemical reaction and not catalyze them.
  5. Enzymes are never consumed in the reactions whereas hormones are used up int he reactions.
  6. Chemical nature of enzymes remain unchanged in reactions whereas chemical nature of hormones are changed in the reactions.
  7. Enzymes always have high molecular weight whereas hormones are generally low molecular weight compounds.
  8. Enzymes produce reversible changes in the substrate whereas changes induced by the hormones are irreversible.

Biological significance of Enzymes

The biological significance of enzymes are:

  1. Healing of wound : A protein digesting enzyme obtained from pancreas of the pig is very useful for skin diseases and healing of wound. These enzymes dostroy protein digesting enzymes of human body thus help for healing of wound.
  2. Dehairing of hides : Enzymes obtianed from pancreas destroy hair follicles of hair, thus help for removal of hair from hide.
  3. Dissolving the blood clot : An enzyme called as urokinase obtained from urea helps to dissolve blood clot which are formed int he brain or arteries, thus saves our life.
  4. Changing blood group : Prof. Hen Furunkawa in 1981 explained that the blood groups are determined by the presence of sugars found in R.B.C.s for which specific enzymes are found. If these enzymes are destroyed, then blood group A and B can be changed into blood group O.
  5. Cheese making : Animal rennin is used in cheese making.
  6. Manufacture of fruit juice : Some enzymes are used for processing of some fruit juices. Pectic enzymes are added to these fruit juices to make it clean and clear.

Last words

In these two articles, Enzymes part I and enzymes part II, you have read detail about enzymes. The study of enzymes will be useful for the students of middle and higher secondary level. This article will also be useful for the students of college level.


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