BIOCHEMISTRY

1. ENZYME
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2. Syllabus

3. INTRODUCTION
Enzymes
3

4. INTRODUCTION
4
• Enzymes are biocatalysts – the catalysts of life.
• A 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.

5. 5
PROPERTIES

6. 6
PROPERTIES
• They are protein in nature
• colloidal
• thermolabile in character
• specific in their action.

7. PROPERTIES
• The functional unit of the enzyme is known as holoenzyme
• Holoenzyme made up of apoenzyme (the protein part) and a
• coenzyme (non-protein organic part).
Holoenzyme
(active enzyme)
Apoenzyme + Coenzyme
(protein part) (non-protein part)
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8. STRUCTURE OF ENZYMES
the region that binds
 The active site of an enzyme is
substrates, co-factors and prosthetic groups and contains
 Active site has a specific
protein.
shape due to tertiary structure of
 A change in the shape of protein affects the shape of active
site and function of the enzyme.

9. ACTIVE SITE
Binding Site
It chooses the substrate
and binds it to active site.
Catalytic Site
It performs the catalytic
action of enzyme.
o Active site can be further divided into:
Active Site

11. INORGANIC CO-FACTORS
o These are the inorganic molecules required for the proper
activity of enzymes.
ORGANIC CO-FACTORS
o These are the organic molecules required for the proper
activity of enzymes.

12. TYPES OF ORGANIC CO-FACTORS
Prosthetic Group Coenzyme
o A prosthetic
tightly bound
group is a o A coenzyme is
organic co-
bound organic loosely
co-facto+r.
E.g. NAD+
factor e.g. Flavins, heme
groups and biotin.

13. SUBSTRATE
 The reactant in biochemical reaction is termed as substrate.
 When a substrate binds to an enzyme it forms an enzyme-
substrate complex.
Enzyme
Joins
Substrate

14. CLASS
• Enzymes are sometimes considered under two broad
categories :
(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.

15. NOMENCLATURE OF ENZYMES
o An enzyme is named according to the name of the substrate it
catalyses.
o Some enzymes were named before a systematic
naming enzyme was formed.
Example: pepsin, trypsin and rennin
way of
o By adding suffix -ase at the end of the name of the
substrate, enzymes are named.
o Enzyme for catalyzing the hydrolysis is termed as hydrolase.

16. EXAMPLE
substrate enzymes products
lactose lactase glucose + galactose
maltose maltase Glucose
cellulose cellulase Glucose
lipid lipase Glycerol + fatty acid
starch amylase Maltose
protein protease Peptides +
polypeptide

17. CLASSIFICATION
• The International Union of Biochemistry (IUB) appointed
an Enzyme Commission in 1961.
• Since 1964, the IUB system of enzyme
classification has been in force.
• Enzymes are divided into six major classes (in that
order).
• Each class on its own represents the general type of reaction
brought about by the enzymes of that class

19. [The wordOTHLIL (first letter in each class) may be memorised
to remember the six classes of enzymes in the correct order].
• Each class in turn is subdivided into many sub- classes which are further
divided.
• A four digit Enzyme Commission (E.C.) 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.

20. • The contact between the enzyme and substrate is
the most essential pre-requisite for enzyme activity.
Factors affecting Enzyme

22. Factors affecting Enzyme

23. 1. Concentration of enzyme
• As the concentration of the enzyme is increased, the
velocity of the reaction proportionately increases
Factors affecting Enzyme

24. 2. Concentration of substrate
• Increase in the substrate concentration gradually
increases the velocity of enzyme reaction within the
limited range of substrate levels.
• A rectangular hyperbola is obtained when velocity is
plotted against the substrate concentration .
Factors affecting Enzyme

25. 3. Effect of temperature
• Velocity of an enzyme reaction
increases with increase temperature
up to a maximum and then declines.
• A bell-shaped curve is usually observed .
• Temperature coefficient or Q10 is defined as
increase in
enzyme velocity when the temperature is
increased by 10°C.
Factors affecting Enzyme

26. 4. Effect of pH
•Increase in the hydrogen ion concentration (pH) considerably
influences the enzyme activity and a bell-shapedcurve is
normally obtained
• Each enzymehas an optimum pH at
which the velocity is maximum. Below and
above this pH, the enzyme activity is much lower and at
extreme pH, the enzyme becomes totally inactive.
Factors affecting Enzyme

27. 5. Effect of product concentration
• The accumulation of reaction products generally
decreases the enzyme velocity.
• For certain enzymes, the products combine with the
active site of enzyme and form a loose complex and,
thus, inhibit the enzyme activity.
Factors affecting Enzyme

28. 6. Effect of activators
• Some of the enzymes require certain inorganic metallic cations like Mg2+, Mn2+, Zn2+, Ca2+,
Co2+, Cu2+, Na+, K+ etc. for theiroptimum activity.
• Rarely, anions are also needed For enzyme activity e.g. chloride ion
• Two categories of enzymes requiring metals for their activity are distinguished
1. Metal-activated enzymes : The metal is not tightly held by the enzyme and can be
exchanged easily with other ions e.g. ATPase (Mg2+ and Ca2+) Enolase (Mg2+)
2.Metalloenzymes : These enzymes hold the metals rather tightly which are not readily
exchanged.
Factors affecting Enzyme

29. 7. Effect of time
• Under ideal and optimal conditions (like pH, temperature etc.), the time
required for an enzyme reaction is less.
• Variations in the time of the reaction are generally related to the
alterations in pH and temperature.
Factors affecting Enzyme

30. 8. Effect of light and radiation
• Exposure of enzymes to ultraviolet, beta, gamma and X-
rays inactivates certain enzymes due to the formation
of peroxides. e.g. UV rays inhibit salivary amylase
activity.
Factors affecting Enzyme

32. • Enzyme kinetics is the study of the chemical
reactions that are catalysed by enzymes.
• In enzyme kinetics, the reaction rate is measured and
the effects of varying the conditions of the reaction is
investigated.
• Studying an enzymes kinetics in this way can reveal
the catalytic mechanism of this enzyme

36. • Km value is a constant and a characteristic feature of a given enzyme.
• A low Km value indicates a strong affinity between enzyme and
substrate, whereas a high Km value reflects a weak affinity between
them.
• For majority of enzymes, the Km values are in the range of 10–5 to 10–2
moles.
• It may however,be noted that Km is not dependent on the
concentration of enzyme.

37. Lineweaver-Burk doublereciprocal plot:
• For the determination of Km value, the substrate saturation curve
(Fig.) is not very accurate
• since Vmax is approached
asymptotically.
•By taking the reciprocals of
the equation (1), a
straight line graphic representation is
obtained.

38. Lineweaver-Burk doublereciprocal plot:

39. REGULATION OF ENZYME
Enzyme regulation definition: “Process, by which cells can
turn on, turn off, or modulate the activities of various
metabolic pathways by regulating the activity of enzyme”

40. WHAT DO
YOU
UNDESTAND
BY
REGULA
TION
OF ENZYME

41. • Enzyme regulation is the control of the rate of a reaction
catalyzed by an enzyme by some effector (e.g., inhibitors or
activators) or by alteration of some condition (ph or ionic
strength)

42. • There are many kinds of molecules that block or
promote enzyme function, and that affect enzyme
function by different routes.

43. ENZYME INHIBITORS
WITH EXAMPLES
An enzyme inhibitor is a
molecule/substance that binds to an
enzyme and blocks its activity.

44. TYPES
Types of enzyme inhibition:
competitive, noncompetitive, and
uncompetitive.

45. COMPETITIVE VS NON COMPETITIVE

46. COMPETITIVE VS NON COMPETITIVE
Competitive
Examples –
Enzyme- lactate dehydrogenase
Substrate- lactate
Inhibitor- Oxamate
The enzyme of Krebs cycle succinate
dehydrogenase catalyzes a reaction to
convert succinate into fumarate. Malonate
acts as a competitive inhibitor because it
has a similar structure to succinate, the
inhibitor binds to the active site of
succinate dehydrogenase and inhibits the
reaction.
Noncompetitive
Cyanide action on cytochrome oxidase is an
example of non-competitive inhibition

47. Clinically Important Isoenzymes
ENZYME PROFILE INLIVER DISEASE
Enzymes are commonly studied for diagnose liver diseases:
1. Alanine aminotransferase (ALT)
2. Aspartate aminotransferase (AST)
3. Alkaline phosphatase (ALP)
4. Nucleotide phosphatase (NTP)
5. Gamma glutamyl transferase (GGT)

48. Enzyme inhibitor is a molecule that lowers the activity of an
enzyme by binding with the active site of the enzyme.
It reduces the amount of products.
Enzyme inducer is a molecule that increases the activity of an
enzyme either by binding to the enzyme or by increasing the
synthesis of the enzyme.
Enzyme repression refers to a decrease in enzyme after a stimulus.
Allosteric enzymes are enzymes that have an additional binding site
for effector molecules other than the active site.

49. 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.
• Regulated by exposure to drugs and environmental
chemicals leading to increased rates of metabolism.
• The cholesterol pathway provides examples of enzyme
induction. A lack of cholesterol leads to an increased synthesis of
HMG-CoA reductase, an example of enzyme induction.

50. ENZYME REPRESSION
Enzyme repression is the mode by which the synthesis of an
enzyme is prevented by repressor(small protein molecule)
molecules.
The cholesterol pathway provides examples of enzyme
induction and repression

51. ALLOSTERIC ENZYMES REGULATION
• Allosteric enzymes are enzymes that have an additional binding
site for effector molecules other than the active site.
• The binding brings about conformational changes, thereby
changing its catalytic properties. .

52. Therapeutic and diagnostic applications of enzymes
and isoenzymes
Isozymes are enzymes that differ in amino acid sequence but catalyze
the same chemical reaction.

53. ENZYME APPLICATION IN THERAPEUTICS
•Certain enzymes can be used to treat several diseases, e.g.:
• Certain types of leukemia are treated with bacterial
asparaginase.
• Dermal ulcers and severe burns can be cleaned with
collagenase by removing dead tissue.
• Penicillinase - Treats patients who have an allergy to
penicillin.
• Streptokinase and urokinase - To dissolve a clot caused by
myocardial infarctions.
• GIT disorders and chronic pancreatitis are treated with
pepsin, lipase, amylase elastase, and trypsin peptidase.

54. Isoenzymes
• Isoenzymes or isozymes are multiple forms of same
enzyme that catalyze the same chemical reaction
• Different chemical and physical properties:
• Kinetic properties
• Amino acid sequence
• Amino acid composition
• Multiple forms of the same enzyme will also help in the
regulation of enzyme activity, Many of the isoenzymes are
tissue-specific. Although isoenzymes of a given enzyme
catalyse the same reaction, they differ in Km, Vmax or
both. e.g.isoenzymes of LDH and CPK.

55. Clinically Important Isoenzymes
LACTATE DEHYDROGENASE
It has five isoenzymes present in blood, ie.,
1.LDH1 (HHHH) specific for heart--faster
2.LDH2 (HHHM) RBCs--faster
3.LDH3 (HHMM) brain--fast
4.LDH4 (HMMM) Liver--slow
5.LDH5 (MMMM) Muscle--slowest

56. Clinically Important Isoenzymes
CREATINE KINASE (CK)
Three isoforms are present, i.e.,
1.CK1 (BB) (brain)
2.CK2 (MB) (heart)
3.CK3 (MM) (skeletal muscle)
In myocardial infarction (MI) there is elevation of total CK with
marked elevation of CK2 (MB) after 4-8 hours.
Electrophoresis is important to detect which fraction increased.
CK2 is used for early detection.
LDH1 for follow-up

57. ENZYME APPLICATION IN DIAGONSITIC
Liver, cardiac and skeletal enzyme markers:
•Important markers that we are going to see are,
• Transaminase or aminotransferase.
• Alkaline phosphatase.
• Glutamate dehydrogenase (GLD).
1.Transaminase or aminotransferase:
•Elevated levels of Aspartate aminotransferase (AST) and plasma alanine aminotransferase
(ALT) are found to indicate liver disease.
•As AST concentration in heart muscle is relatively high after myocardial infarction, AST
level increases.

58. ISOENZYME APPLICATION
•Diagnosis of diseases:the measurement of serum alkaline
phosphatase (ALP) and gamma-glutamyl transferase (GGT)
levels can help diagnose liver and bone diseases.
•Prognosis of diseases: Isoenzymes can also be used to
predict the outcome of a disease or the response to therapy.
For example, the ratio of two isoenzymes of lactate
dehydrogenase (LDH) can help predict the outcome of
testicular cancer.

59. ISOENZYME APPLICATION
Monitoring of therapy: Isoenzymes can be used to monitor
the response to therapy or the recurrence of a disease. For
example, the measurement of serum thyroglobulin (Tg) levels
can help monitor the recurrence of thyroid cancer.
Targeted therapy: Isoenzymes can be targeted by drugs to
achieve selective effects on specific tissues or organs. For
example, selective inhibitors of cyclooxygenase-2 (COX-2)
isoenzyme are used to treat inflammation and pain

61. DEFINE & FUNCTION
Define-Coenzymes are a type of cofactor and they are
bound to enzyme’s active sites to aid with their proper
functioning.
The function of coenzymes is to transport groups between
enzymes

62. Important coenzyme
• Alcohol dehydrogenase
• Coenzyme A
• Flavin adenine dinucleotide (FAD)
• Nicotinamide adenine dinucleotide (NAD)
• Adenosine triphosphate (ATP)

63. Adenosine triphosphate (ATP)
• The function of ATP is to transport chemical energy
within cells for metabolism.
• ATP is often referred to as the energy currency of cells.
• Adenosine triphosphate is composed of an adenine
nucleotide base, a ribose sugar and three phosphate
groups.
• Energy can be released from ATP when the terminal
phosphate group is released in a hydrolysis reaction.

64. END…..