This unit consists of the topics mentioned in PCI syllabus which is prescribed in various pharmacy colleges all over india.

1. UNIT-5
Enzymes
Introduction, properties, nomenclature and IUB classification of
enzymes.
Enzyme kinetics (Michaelis plot, Line Weaver Burke plot)
Enzyme inhibitors with examples.
Regulation of enzymes: enzyme induction and repression,
allosteric enzymes regulation.
Therapeutic and diagnostic applications of enzymes and
isoenzymes.
Coenzymes –Structure and biochemical functions.
BY : Dr. Anjana Sharma,
Associate Professor,
MIET, Meerut

2. ENZYMES:
Enzymes are the biocatalysts that increase the rate
of reaction without itself undergoing any change in
the overall process.
Eg: aminotransferases, kinases.
***The functional enzyme is referred as
(holoenzyme) which is made up of protein part
(apoenzyme)
The co-enzymes are non-protein compound that is
necessary for the functioning of an enzyme. Eg:
NAD+ (Nicotinamide adenine dinucleotide), CoA (
Coenzyme A).
1

3. ACTIVE SITE:
The active site or active centre of an enzyme , is an
area at which the substrate binds and participates in
catalysis. It has two sites:
1. Binding site: Substrate binds to active site.
2. Catalytic site: Which performs catalysis
2

4. The co-enzymes or cofactors are non-protein compound
that is necessary for the functioning of an enzyme. Eg:
NAD+ (Nicotinamide adenine dinucleotide), CoA (
Coenzyme A).
3

5. CLASSIFICATION & NOMENCLATURE
(i) All known enzymes have been grouped into six major classes on the basis of
reaction type they catalyze,
(ii) Each class further sub-divided into subclasses and sub-subclasses,
(iii) Each enzyme is assigned two names i.e., recommended (trivial) name and
systematic name,
(iv) Each enzyme is identified by a unique four digit classification number.
For example, hexokinase is recommended name, its systematic name is glucose
phosphotransferase and its classification number in EC 2.7.1.1. Here, “EC” stands
for Enzyme commission,
the first number (2) stands for the major class,
the second number (7) stands for the sub class,
the third number (1) indicates sub-class and
the fourth number (1) denotes the serial number assigned in its sub-classes.

6. NOMENCLATURE OF THE ENZYMES:
I- INTRACELLULAR ENZYMES = NON-FUNCTIONAL
PLASMA ENZYMES
II-EXTRACELLULAR ENZYMES = FUNCTIONAL
PLASMA ENZYMES-DIGESTIVE ENZYMES
ENZYME NAME = SUBSTRATE + ASE

8. FACTORS AFFECTING ENZYME ACTIVITY
1. Factor 1: Concentration of Enzyme
As the concentration of the enzyme is increased, the velocity of the reaction
proportionately increases. This property is used for determining the activities of
serum enzymes during the diagnosis of diseases.

9. FACTOR 2: CONCENTRATION OF SUBSTRATE

10. FACTOR 3: EFFECT OF TEMPERATURE
The enzyme activity gradually lowers as the temperature rises more than the optimal
temperature until it reaches a certain temperature at which the enzyme activity stops
completely due to the change of its natural composition. the optimal temperature,
which ranges between 37 to 40C°.

11. FACTOR 4: EFFECT OF PH
Enzymes are protein substances that contain acidic carboxylic groups (COOH–) and
basic amino groups (NH2). So, the enzymes are affected by changing the pH value.

12. FACTOR 5: EFFECT OF ACTIVATORS
Some of the enzymes require certain inorganic
metallic cations, like
Mg2+, Mn2+, Zn2+, Ca2+, Co2+, Cu2+, Na+, K+ etc.,
for their optimum activity.
Rarely, anions are also needed for enzyme
activity, e.g. a chloride ion (CI–) for amylase.

13. EFFECT OF SUBSTRATE CONCENTRATION (MICHAELIS
MENTEN EQUATION

17. ENZYME INHIBITION
An enzyme inhibition is a process by which any substance
binds with the enzyme and decreases the catalytic activity of
enzyme.
Reversible
Irreversible
Allosteric
Types of inhibition
Competitive inhibition
Non-Competitive inhibition

21. ENZYME INDUCTION & REPRESSION:
Enzyme Induction: A process in which a molecule (e.g. a drug) induces (i.e. initiates
or enhances) the expression of an enzyme. An enzyme inducer is a type of drug
which binds to an enzyme and increases its metabolic activity. Example: lac operon
Examples of Enzyme Induction: The insulin hormone induces the synthesis of
glycogen synthetase, glucokinase, phosphofructokinase, and pyruvate kinase. All
these enzymes are involved in the utilization of glucose. Also, the hormone cortisol
induces the synthesis of various enzymes e.g. pyruvate carboxylase, tryptophan
oxygense, and tyrosine aminotransferase.
Enzyme repression: Effectors can associate with the operator and alter the
configuration so that the binding of the polymerase occurs less efficiently or not at
all. This effect is known as repression. Example: trp operon
Examples of Enzyme repression: In many cases substrate can repress the synthesis of
many enzymes. Pyruvate carboxylase is the key enzyme in the synthesis of glucose
from non-carbohydrate sources like pyruvate and amino acids. If there is sufficient
glucose available there is no necessity of its synthesis. This is achieved by the
repression of pyruvate carboxylase by glucose.

22. Allosteric regulation:
•Allosteric enzyme have one or more allosteric sites
•Allosteric sites are binding sites distinct from an enzyme
active site or substrate binding site
•Molecule that bind to allosteric sites are called effector or
modulator
•Effector may be positive or negative, this effector regulate
the enzyme activity. The enzyme activity is increased when a
positive allosteric effector binds at the allosteric site known as
activator site. On the other hand, negative allosteric effector
bind at the allosteric site called inhibitor site and inhibit the
enzyme activity.
•Binding to allosteric sites alter the activity of the enzyme,
this is called cooperative binding.

23. TYPES OF ALLOSTERIC REGULATION
•Heterotropic : A heterotropic allosteric modulator is a
regulatory molecule that is not also the enzyme's
substrate. It may be either an activator or an inhibitor of
the enzyme.
For example, H+, CO2, and 2,3-bisphosphoglycerate are
heterotropic allosteric modulators of hemoglobin
•Homotropic: A homotropic allosteric modulator is a
substrate for its target enzyme, as well as a regulatory
molecule of the enzyme's activity. It is typically an
activator of the enzyme.
For example, O2 is a homotropic allosteric modulator of
hemoglobin.

24. ISOENZYMES
Isoenzymes are enzymes that catalyze the identical chemical reactions but they differ
in their aminoacid sequence. They have different kinetic parameters or Km values or
different regulatory properties.
•They are used in the diagnosis of cardiac disease, Muscle disease, Bone disease,
hepatic disease
•LDH isoenzymes: It is test to check how much lactate dehydrogenase in the blood.
•They increase in myocardial infarction, Lung infarction, Hemolytic anemia,
Megaloblastic anemia, Acute pancreatitis, hypothyroidism.
•CPK isoenzymes : creatine phosphokinase , Creatine Kinase
CPK-1: higher than normal level in Brain cancer, brain injury, Electroconvulsive therapy,
Seizures.
CPK 2: Heart attack (there is significant rise in CPK-2 in firs 2-3 hrs. after a heart
attack), Myocarditis, Electrical injuries, Open heart surgeries, Heart fibrillation.
CPK 3:
Crush injuries of muscle, Muscular dystrophy, Myositis, Sternous exercise

27. VITAMINS AS CO-ENZYMES:
Vitamins (water soluble vitamin, fat soluble vitamin): an
organic substance needed in small amounts for normal
body functions that the body cannot synthesize in
adequate amounts
The vitamins are of two distinct types: water soluble and fat
soluble.
Water Soluble Vitamins : Thiamine (B1), Riboflavin (B2),
Niacin (B3), Pantothenic Acid (B5),
Pyridoxal, Pyridoxamine, Pyridoxine (B6), Biotin, Cobalamin
(B12) ,Folic Acid, Ascorbic Acid (Vitamin C)
Fat Soluble Vitamins : Vitamin A, Vitamin D, Vitamin E,
Vitamin K

28. •The vitamins cannot be synthesized
by mammalian cells and therefore
must be supplied in the diet in the
small quantities.
•Protein+coenzyme(vitamin) enzyme
•Protein+cofactor(metal ion) enzyme

29. THIAMINE (VITAMIN B1)
• It is a substituted pyrimidine & thiazole which is linked by methlyene
bridge (-CH2).
•It gets converted into active form Thiamine pyrophosphate (TPP).
Role of Thiamine :
•It act as a cofactor for pyruvate dehydrogenase and alpha-ketoglutarate
dehydrogenase.
•It involves in transketolase catalysed reactions in pentose phophate
pathway for transferring aldehyde or ketone group.

30. RIBOFLAVIN (VITAMIN B2)
•It is the precursor for the coenzymes, flavin mononucleotide (FMN)
and Flavin adenine dinucleotide (FAD).
•Enzymes that require FMN & FAD as cofactors are known as
flavoproteins.
•They are involved in redox reactions eg: succinate dehydrogenase &
xanthine oxidase. The reduced form of FMN & FAD are FMNH2 and
FADH2 respectively.

31. NIACIN (VITAMIN B3)
•Active form of Vit B3 is Nicotinamide adenine dinucleotide(NAD) and Nicotinamide
adenine dinucleotide phosphate (NADP).
•They take part in oxidation reactions of our body.
•The NAD is required as a coenzyme for pyruvate dehydrogenase complex and alpha-
ketoglutarate dehydrogenase complex to mediate the reactions.
•The NADP is required as a coenzyme for glucoe-6-phosphte dehydrogenase and
6-phosphate gluconate dehydrogenase-mediated reactions.

32. VITAMIN B5 (PANTOTHENIC ACID)
FUNCTIONS:
•Active form is coenzyme (CoA-SH) form
•Its reactive group is sulfhydryl group (-SH)
•CoA-SH is required for the conversion of pyruvate to actyl CoA
by pyruvate dehydrogenase complex
•Fatty acid to acyl CoA by thiokinase.

33. PYRIDOXINE (VITAMIN B6)
Functions:
•It acts as coenzyme in
Transamination reactions
Glycogenolysis
Synthesis of neurotransmitter gamma amino butyric acid (GABA).

34. FUNCTIONS:
•Biotin itself act as coenzyme.
•It functions as a coenzyme in the carboxylation reactions .
For eg: 1. acetyl CoA to malonyl CoA
2. pyruvate to oxaloacetate.

35. FOLIC ACID
Functions:
• The active form of folic acid is tetrahydrofolic acid (THF).
•The is a carrier of single carbon and is involved in single
carbon transfer reactions.
•The single carbon may be in the form of formyl (-CHO), methyl
Methylene or formimino group.

36. VITAMIN B12 (COBALAMIN)
• It consist of of four pyrrrole ring (Corrin ring) and
Cobalt ion in the centre.
• Methylcobalamin and 5’deoxyadenosylcobalamin
are the two active form of cobalamin.
• Methylcobalamin is required in the conversion of
homocysteine to methionine.

37. THANK YOU !!!