At the end of this lecture, student will be able to

• Explain definition and nomenclature

• Classify enzymes

• Describe properties of enzymes

• Explain the therapeutic applications of coenzyme


• Enzymes are biocatalysts – the catalysts of life

• Catalyst is defined as a substance that increases the
velocity or rate of a chemical reaction without itself undergoing any change in the overall process

• Enzymes may be defined as biocatalysts synthesized by
living cells, protein in nature, colloidal and thermolabile in character and specific in their action

• In the laboratory, hydrolysis of proteins by a strong acid
at 100oC takes at least a couple of days & same protein is fully digested by the enzymes in gastrointestinal tract at body temperature (37oC) within a couple of hours due to enzymes

Nomenclature and classification of enzymes

• In the early days, the enzymes were given names by their
discoverers in an arbitrary manner e.g. pepsin, trypsin, chymotrypsin (convey no information about the function of the enzyme or the nature of the substrate on which they act

• Sometimes suffix-ase was added to the substrate for naming the enzymes e.g. lipase acts on lipids; nuclease on nucleic acids; lactase on lactose

• These are known as trivial names of the enzymes which,
however, fail to give complete information of enzyme reaction

• Enzymes are sometimes considered under two broad

(a) Intracellular enzymes – They are functional within cells
where they are synthesized

(b) Extracellular enzymes – These enzymes are active outside the cell; all the digestive enzymes belong to this group

• The International Union of Biochemistry (lUB) appointed an
Enzyme Commission in 1961

• This committee made a thorough study of the existing
enzymes and devised some basic principles for the classification and nomenclature

• Since 1964 the IUB system of enzyme classification has
been in force

• Enzymes are divided into six major classes

1. Oxidoreductases: Enzymes involved in oxidation-reduction reactions

2. Transferases: Enzymes that catalyse the transfer of functional groups

3. Hydrolases: Enzymes that bring about hydrolysis of various compounds

4. Lyases: Enzymes specialised in the addition or removal of water, ammonia, CO2 etc

5. lsomerases: Enzymes involved isomerization reactions

6. Ligases: Enzymes catalysing the synthetic reactions. Where two molecules are joined together and ATP is used

Nomenclature and classification of enzymes

• Each class in turn is subdivided into many sub-classes
which are further divided

• A four digit Enzyme Commission (EC) number is assigned to each enzyme representing the class (first digit), sub-class (second digit), sub-sub class (third digit) and the individual enzyme (fourth digit)

• Each enzyme is given a specific name indicating the substrate, coenzyme (if any) and the type of the reaction catalysed by the enzyme

• Although the IUB names for the enzymes are specific and
but they have not been accepted for general use as they are complex and cumbersome to remember

• Therefore, the trivial names, along with the E.C. numbers as and when needed, are commonly used and widely accepted

Properties of enzymes

• All the enzymes are invariably proteins, however, few RNA
molecules have been shown to function as enzvmes

• Each enzyme has its own tertiary structure and specific
conformation which is very essential for its catalytic activity

• The functional unit of the enzyme is known as holoenzyme
which is often made up of apoenzyme (the protein part) and a coenzyme (non-protein organic part)

Holoenzyme → Apoenzyme + Coenzyme

(Active enzyme) → (protein part) + (non-protein part)

• The term prosthetic group is used when the non-protein
moiety tightly binds with the apoenzyme & coenzyme can be separated by dialysis from the enzyme while the prosthetic group cannot be

• The term monomeric enzyme is used if it is made up of a
single polypeptide e.g. ribonuclease, trypsin

• Some of the enzymes possess more than one polypeptide
chain are known as oligomeric enzymes e.g. lactate dehydrogenase

• Enzymes form colloidal solutions instead of true solution
in water

• Enzymes vary in their molecular weight

• Enzymes can be precipitated by dehydrogenation or

• Based on enzyme complex, wide variations in the enzyme

• By biotechnology it is possible to modify enzyme with
desirable characters to improve catalytic activity under unusual condition

• The enzymes exhibit all the general properties of proteins

• Enzymes possess enormous potential use in medicine and industry in genetic manipulations and industrial applications

Application of enzymes

• Decreased in plasma enzymes in certain diseases

Application of enzymes


• Enzymes are biocatalysts – the catalysts of life

• Enzymes are divided into six major classes; oxidoreductases, Transferases, Hydrolases, Lyases, lsomerases and ligases

• The functional unit of the enzyme is known as holoenzyme
which is often made up of apoenzyme and a coenzyme

• Enzymes are used as therapeutic agents, as analytical
reagents, in genetic manipulations, in industrial applications and in diagnosis of diseases

Also, Visit:

B. Pharma Notes | B. Pharma Notes | Study material Bachelor of Pharmacy pdf

B. Pharma Handwritten Notes

B. Pharma PDF Books

B. Pharma Lab Manual

D. Pharma Lab Manual

B. Pharma 8th Semester Previous Year Question Paper

D. Pharma Notes

Leave a Comment