• Enzymes are substances which can speed up rate of rate of biochemical reactions.
  •  Enzymes are also known as biological catalysts. Enzyme can accelerate both rate and specificity of metabolic reactions and hence they are highly selective catalysts.
  • Most of the enzymes end with suffixase. There are few exceptions like Ptyalin, trypsin and pepsin. The names of the enzymes are given based on chemical reaction they carry out and also on the basis of substrate to which it acts. This whole process is known as Nomenclature of enzymes.


  • To represent Ferments (process of fermentation-sugar to alcohol conversion) in the year 1878 F.W Kuhne coined the term enzyme.
  • In the year 1903, first ever enzyme was isolated by E. Buchner. In the year 1926 urease enzyme was purified and obtained in its crystalline form. This work demonstrated protein nature of enzyme and was given by James Sumner.

Properties of enzymes:

  • Enzymes are considered as proteins and nearly all enzymes are proteins, although catalytically active few RNA molecules have been identified.
  • Mild conditions are typically required by enzymes for their catalysis (temperatures below 100 degree Celsius, neutral pH and atmospheric pressure).
  • Enzymes acts as catalyst and speed up chemical reaction without being altered by itself in the process.
  • Enzymes are highly specific and acts on specific substrates.
  • Based on the concentration of substrates, activity of enzymes can be regulated.
  • Enzymes can form hydrosols in Free State and are hydrophilic in nature.
  • Turn over(kcat) number of enzymes can be defined as number of substrate molecules altered per minute by an enzyme. If the turn over number is high, enzyme will be more efficient.
  • Nature of enzymes is reversible. Energy requirements, availability of reactants, concentration and pH of products are some factors upon which reversibility of enzyme depends.
  • Specific confirmation for holding and binding to substrates is present at the active site of an enzyme.
  • Enzymes require optimum temperature of around 25-35 degree Celsius and most of the enzymes are heat sensitive (thermo labile). 

Characteristics of enzymes:

  • Holoenzyme: If an enzyme is combined with a co-enzyme (non-protein moiety) it forms holoenzyme. It is catalytically active. Example- DNA and RNA Polymerases.
  • Apoenzyme: It is an inactive enzyme but gets activated when an organic or in-organic co-factor binds to it. Example: Apoglucose oxidase (Can be extracted from Aspergillus Niger).
  • Co-enzyme: It is a non-protein compound and is essential for the activity of enzyme. Co-enzymes can be separated from apoenzymes. Example: S- adenosyl metheionines.
  • Prosthetic group: It is a non-protein component of any conjugated protein. If a substance is attached covalently to the protein part of an enzyme it is called as prosthetic group.      Examples- flavin, biotin, heme.
  • Activator: Generally metal ions (Mg, Mn, and Zn) are designated as activators. They form a co-ordination complex between substrate and enzyme. They can also activate the substrate by inducing electronic shifts.
  • Zymogens: They are secreted in inactive forms and are generally simple protein enzymes. Examples: Trypsinogen, Pepsinogen.

Mechanism of enzyme action:

  • Multiple weak forces present in the active site binds the substrate which results in the formation of enzyme-substrate complex.
  • Once the substrate molecule gets binded, active residues present in the active site of enzyme acts on substrate molecule and transforms it into transition state complex and then to products, which are released.
  • Now, after the release, enzyme is free to bind another substrate molecule to begin its catalytic cycle again.

Substrate-Enzyme Binding:

  • Substrate binds to the active site of an enzyme and active site converts the substrate into products. It is a three dimensional entity made up of amino acid residues.
  • Substrate-Enzyme binding is explained with the help of two famous models:
  • Lock and Key Model:
  • Based on the name, the model explains that the substrate and the active site of enzyme fits together like a key (substrate) into its lock (active site). The theory was proposed in the year 1894 by Emil Fischer.
  • Shapes formed are considered as Rigid and fixed and compliments each other when brought together in a right alignment.
  • Induced Fit Model:
  • When substrate binds to active site it induces a conformational change in the active site of enzyme. This theory was proposed in the year 1958 by Daniel E. Koshland.
  • The theory also states that, enzyme may distort the substrate, which forces the enzyme into a conformational change similar to transition state. Example- Glucose binding to hexokinase.

Classification of Enzymes:

  • Oxidoreductases: It can catalyze oxidation-reduction reactions in which electron transfer takes place. These electrons are usually hydrogen atoms or hydride ions.
  • Transferases: It is involved in transfer reaction from donor molecule to acceptor molecule. Example- Hexokinase used in glycolysis.
  • Hydrolases: Involves transfer of functional groups to water. It generally catalyzes reactions that involves hydrolysis. Example- Chymotrypsin.
  • Lyases: when functional groups are added to break double bonds in molecules, lyases enzymes can be used. Example- fructose biphosphate aldolase (converts fructose 1, 6 bisphosphate to G3P and DHAP by cutting the C-C bond.
  • Isomerases: As the name suggest, they catalyzes transfer of functional groups within a molecule and forms isomeric structures. They allow structural and geometric changes within a compound. Example- Phosphogluco-isomerase.
  • Ligases: Used in joining of two substrates. They are coupled to cleavage of ATP.

Enzymes play an important role in normal metabolism. If enzymes are absent, biochemical processes won’t work. They tend to increase the rate of reaction and essential components in living systems.

Role of enzymes in detergents:

  • Detergents combines with dirt and impurities and makes them soluble. Detergents are water soluble cleansing agents.
  • One main reason in using enzymes for detergents is that they are capable of removing stains at lower temperatures and reduces water consumption.
  • Enzymes are obtained from renewable sources and hence are environment friendly and are incorporated with detergents to minimize the usage of chemicals.
  • Use of toxic compounds also reduces if enzymes are used in detergent formulations.
  • Efficiency of cleaning increases by using enzymes, as number of wash cycles can be reduced.
  • Most common type of enzymes used in detergent formulations are Proteases.
  • Enzymes used in detergents must be effective at alkaline pH, should be able to withstand wide range of temperatures.
  • When enzymes are used in different combinations efficiency of cleaning can be improved drastically. About 80% of detergents in market contains an enzyme or combination of enzymes.

Enzymes used in detergents:

  • Proteases: Hydrolyses of peptide bonds is catalyzed by proteases. In protein based stains, these proteases cleaves peptide bonds. Most common type of protease used in detergent formulation is alkaline serine proteases.
  • Lipases: Triglycerides ester bonds are broken in oil-water interface and hydrolyzes it into mono and diglycerides. Thermostable lipases has been used as additives in detergents. Lipolase was the first detergent based lipase introduced by Novo Nordisk in the year 1988. The other enzymes used in detergents are Amylases, Mannanases, and cellulases.


                   BY: Sreelakshmi S Nair


Proteins are macromolecules obtained from the one or more amino acids chain linked by peptide bonds. They are the natural polymers of amino acids. It contains nitrogen, carbon, hydrogen and oxygen. They act as a biological catalyst form structural parts of different organisms, participate in different cell reactions.


Proteins are classified on the basis of

  • Structure of Protein
  • Composition of Protein
  • Functions of Protein

Based on the structure of Protein

  • Fibrous Protein

They are linear in shape. Usually they do not have tertiary structure. They are physically strong and are insoluble in water. They perform the structural functions in the cell. Examples are: Keratin, Collagen, and Myosin.

  • Globular Protein

They are spherical or globular in shape.Teritary structure is the most functional structure. Physically they are soft while comparing to fibrous proteins. They are readily soluble in water. Most of the proteins present in the cell belongs to globular protein. It forms enzymes, antibodies and some hormones. Examples are Insulin, haemoglobin, DNA polymerase and RNA polymerase.

Based on the composition of Protein

  • Simple proteins

They are composed of only amino acids. They may be fibrous or globular. They are generally simple in structure. Examples are Collagen, Myosin, Insulin

  • Conjugated Proteins

They are complex proteins which contains one or more amino acid components. The non-protein parts are called prosthetic group. Prosthetic group may contain metals, ions, carbohydrates, lipids, nucleic acid. Conjugated proteins are generally water soluble and globular in structure. Most of the enzymes are conjugated proteins.

Based on the Function

  • Structural Proteins

Most of them are fibrous proteins. Components in connective tissue, bone, tendons, cartilage, skin, feathers, nail, hairs and horn are made of structural proteins.

  • Enzymes

They are the biological catalyst. Mostly globular conjugated proteins. Examples are DNA polymerase, Nitrogenase, and Lipase.

  • Hormones

They include proteinaceous hormone in the cells. Examples are Insulin, ACH

  • Respiratory Pigments

They are coloured proteins. All of them are conjugated proteins. Examples are haemoglobin, Mycoglobin.

  • Transport Proteins

They transport the materials in the cell. They form channels in the plasma membrane. They also form a component in blood and lymph in animals.


There are four levels

  1. Primary Structure
  2. Secondary structure
  3. Tertiary Structure
  4. Quaternary Structure
  1. Primary Structure

They give details about the amino acid sequence of a protein. It tells about the number of amino acid residues in the protein and also about the sequence of amino acids. It is stabilized by peptide bonds. Each component of an amino acid is called residue or moiety. It starts from the amino terminal (N) end and ends in the carboxyl terminal(C) end.

  • Secondary structure

It is formed by hydrogen bond between backbones atoms. Three most important secondary structure in protein are:

  • α-helix
  • β- plates
  • β-Turns

α -Helix

It is the most common secondary structure which repeat every 5.4It is the simplest arrangement of a polypeptide chain which was proposed by Puling and Corey in 1954.It is so common because it makes optimal use of internal hydrogen bond. The interactions between the amino acid chains can stabilize or destabilize the α-helix.

                    β- Plates

It is an extended form of a polypeptide chain.Polypetide backbone forms a zigzag structure. Similar to α-Helix structure is stabilized by hydrogen bond. The R-groups of adjacent amino acids protrude from the zigzag structure to the opposite direction forming an alternative pattern. It can be arranged in either parallel or anti-parallel direction.


         It’s a very common in proteins where peptide make a reverse direction. It forms a 180 degree turn involving four amino acids. The carbonyl oxygen of the first residue forms a hydrogen bond with the amino group hydrogen in the fourth amino acid in the turn. Glycine and proline allows the β-Turns frequently.

3. Tertiary Structure

                   The tertiary structure will have a single polypeptide backbone consisting of one or more    secondary structures. It can be defined by atomic coordinates. It is stabilized with the help of both covalent and non-covalent bond.

4. Quaternary Structure

Proteins which have more than one polypeptide subunit and which do not have a permanent (covalent) interaction between the subunits (like disulphide bond) are classified under quaternary structure. Bonds stabilizing quaternary structure includes hydrogen bonds, hydrophilic interactions, hydrophobic interactions, van der Waals interactions. A protein with a single subunit cannot have a quaternary structure.

Functions of Protein

  • Boosts Immune System
  •  Provides Structure
  • Maintains pH
  • Transports and stores nutrients