This presentation is about the kinetics of enzyme action , the Michaelis- Menten Model and kinetics of allosteric enzyme action in a simplified language.

1. By Jyoti Verma
M.Sc. Botany

2. Enzyme Kinetics-
 Enzyme kinetics is the study of enzymatic reaction rate and how
it changes in response to different experimental parameters like
substrate concentration and effect of inhibitors.
 It is an expression of chemical reactions in mathematical terms.
 It is an oldest approach to understand enzyme mechanism.
History-
• First began in 1902 when Andrian John Brown demonstrated
the hydrolysis of sucrose by invertase.
• The next important step of enzyme kinetics made by Leonor
Michaelis and Maud Menten in 1913.They postulated the
existence of intermediate complex.

3. Classification of Chemical
Reactions-
 Order of Reaction- It is given by the sum of powers of concentrations.
1. Zero Order Reaction- The reaction in which the rate of reaction does
not depends on the concentration of the substrate.
R=K [S]
0
2. First Order Reaction- The reaction rate depends on substrate
concentration and the sum of powers should be 1.
R=K [A]
1
3. Second Order Reaction- A reaction is said to be second order when the
sum of powers of concentration is 2.
R=K[A]
1
[A]
1
R=K[A]
2

4. Michaelis - Menten Model of
Enzyme Kinetics-
 In 1913 Leonor Michaelis and Maud
Menten postulated the existence of
enzyme substrate complex based on their
observations on sucrose.
 They proposed-
1. The enzyme combines with substrate to
form enzyme substrate complex (ES
complex).
2. The substrate gets modified to form
product and the product gets associated
with enzyme (EP).
3. The product gets released from the
enzyme.
Leonor Michaelis
Maud Menten

5. • They derived a relationship
between the substrate
concentration and the reaction
rate.
• As the substrate concentration
increases the rate of reaction
increases but upto a certain
limit as all the enzymes gets
saturated so further increase in
substrate concentration does
not have any effect.
• When a graph is drawn
between the substrate
concentration [S] and Vo , a
hyperbolic curve develops.
• These observations can be
expressed mathematically in
the form of equation
commonly known as
Michaelis –Menten Equation.
Michaelis –Menten Curve
- A hyperbolic curve

6. The Michaelis - Menten Constant
 Km represents the concentration of substrate required to half saturate the enzyme.
 Km is a measure of the stability of the ES complex , being equal to the sum of the
rates of breakdown of ES over its formation.
 Lower the Km more efficient the enzyme is ,as it requires very little amount of
substrate to reach half Vmax while higher the Km less efficient the enzyme is, as
it requires more substrate to reach half Vmax .
Turnover Number and Catalytic Efficiency-
• The Turnover number is the number of substrate molecule that are
converted into product per unit time when the enzyme is saturated with the
substrate.
Kcat=Vmax/[E]T
• Catalytic Efficiency = Kcat/Km
• Increase in turnover number (Kcat) or decrease in Km results in enhanced
catalytic efficiency.

7. Lineweaver – Burk Plot
 The Michaelis –Menten curve was not
useful in determining the exact value
of Vmax , So a more representating
graph was suggested by Hans
Lineweaver and Dean Burk.
 They employed a double reciprocal
plot of 1/Vo versus 1/[S] from the
Michaelis–Menten Equation.
 Advantage-More accurate
determination of Vmax
Lineweaver-
Burk Plot

8. Kinetics of Enzyme Inhibition-
 Inhibitor- Any agent that
decreases the velocity of an
enzyme catalyzed reaction.
 Inhibition may be of reversible
or non-reversible type.
1. Competitive Inhibitors- They
compete directly with the
substrate for the active site of
the enzyme.
 This inhibition can be tackled by
the addition of more substrate.
Lineweaver- Burk Plot showing the effect of
competitive inhibitors on enzyme action

9. Kinetics of Enzyme Inhibition-
2. Uncompetitive
Inhibitors-
 These bind only to the
Enzyme –Substrate
complex , as binding of a
substrate to enzyme creates
a binding site for inhibitor.
 In this case Vmax and Km
decreases ..
Lineweaver- Burk Plot showing the
effect of uncompetitive inhibitors
on enzyme action

10. Kinetics of Enzyme Inhibition-
3. Non – Competitive Inhibitors-
 It can combine either with free
substrate or the ES complex.
 They bind to a site other than
active site of the enzyme.
 In this case Vmax decreases and
Km remains unchanged.
Lineweaver- Burk Plot showing the
effect of non-competitive inhibitors
on enzyme action

11. Kinetics of Allosteric enzymes-
 The allosteric enzymes have another site called allosteric site.
 Some molecule binding to allosteric site can act either as
activator or inhibitor.
 They do not follow Michaelis-Menten kinetics instead of
hyperbolic curve they show a sigmoidal curve because a
small change in concentration will bring about a large change
in reaction rate.
Allosteric Enzyme

12. Significance of enzyme kinetics-
 With the help of enzyme kinetics we can determine the
rate of the reaction with the changes in substrate
concentration as well as we can determine the effect of
inhibitors on reaction rate.
 It helps us to explain how enzyme works.
 Helps us to determine how drugs and poisons inhibit the
enzyme activity.
 Helps us to understand enzyme’s role in metabolic
pathway.
 It helps us to predict how enzymes behave in living
organisms.
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