This document provides an overview of enzyme kinetics. It defines important terms like rate constant, substrate concentration, enzyme unit, and Michaelis constant. It describes models used to study enzyme kinetics like the Michaelis-Menten equations and Lineweaver-Burk, Hanes-Woolf, and Eadie-Hofstee plots. It discusses factors that affect reaction rates like pH, temperature, and inhibitors. The document also covers cooperative enzyme systems and multireactant reactions.

1. Kinetics of Enzyme Action
Manjunatha S
II MSc (Botany)
University of Mysore

2. Contents
1.Introduction
2.Important terms
3.Order of the reaction
4.Models to study Enzyme kinetics
5.Conclusion
6.References

3. Introduction
• Enzyme kinetics is the quantitative study of enzyme
catalysis.
• It measure reaction rates and the affinity of enzymes for
substrates and inhibitors.
• Kinetics also provides insight into reaction mechanisms.
• The general principles of chemical reaction apply to
enzyme catalyzed reactions as well

4. Recall
• Rate constant
• Substrate concentration
• Enzyme unit(U)
• Katal (kat)
• Hyperbola
• Slope
• Intercept

5. Consider
A+B P
Where A and B are reactants & P is Product
Rate= - [A]/ t = - [B]/ t = [P]/ t
Rate α [A]f [B]g
As an equation, Rate= k [A]f [B]g
• The exponents ‘f’ and ‘g’ must be determined experimentally and
not necessarily equal to the coefficients of balanced equation.

6. Order of the reaction
It is the sum of all the exponents of reaction
Eg: Consider, A P
Rate = k[A]1
Order is 1, hence First order reaction

7. Models to study Enzyme kinetics
1.Michaelis and Menten equations
2. Lineweaver-Burk plot
3. Hanes-woolf plot
4. Eadie-Hofstee plot

8. K =
k-1+k2
m k1
Michaelis and Menten equations
V=
Vmax [S]
Km+ [S]

10.  The concentration of substrate [S] is much greater than the concentrations of
enzyme [E].
 The rate of formation of ES is equal to that of the breakdown of ES
 Very little accumulation of P, so the formation of enzyme-substrate complex
from E+P is negligible.
Michaelis-menten model is based on following
assumptions.

11. Steady state assumption
E+S ES E+P

12. Lineweaver-Burk plot

13. Hanes-Woolf plot
[S] =
1[S]
+
Km
V Vmax Vmax
The intercept on the [S]/V axis
gives Km/Vmax

14. Eadie-Hofstee plot
V =
V
+
Vmax
[S] Km Km
The intercept on Y- axis
gives Vmax

15. Turn over number
It is the number of substrate molecules converted into the product by an enzyme
molecule in a unit time when the enzyme is fully saturated with substrate.
Represented by Kcat,
unit is S-1
At saturating [S]
Kcat = Vmax/Et

16. 15 micrograms of an enzyme of molecular
weight 30,000 working at Vmax catalyzes the
conversion of 60 micromole of substrate into
product in 3 min. What is the enzyme's turnover
number (in sec-1)?
Problem

17. Kcat/Km ratio called Specificity constant is often thought of
as a measure of Catalytic efficiency.
A comparison of specificity constant for the same enzyme
with different substrates, or for two enzymes with their
different substrates, is widely used as a measure of
enzyme catalytic efficiency.

18. Enzymes are subjected to various kinds
of inhibition

19. Effect of pH &
Temperature on Enzyme
catalyzed reactions.

20. Kinetics of cooperative systems and
are usually allosteric
• Reaction velocity is insensitive to small changes in substrate, inhibitor
concentration.
• Raising the velocity of an enzyme catalyzed reaction from 0.1 Vmax to
0.9 Vmax requires enormous(81 fold) increase in the substrate
concentration(calculated using Michaelis-Menten equation)
• However in cooperative systems like allosteric enzymes, a small
change in one parameter, such as inhibitor concentration brings about
large change in reaction velocity.
• Plot of ‘v’ versus [S] is no longer hyperbolic, but becomes sigmoidal.

22. Kinetics of multireactant systems
E+A+B E+P+Q

23. Conclusion
Enzyme kinetics finds its usefulness in various reactions
mediated by enzymes, which includes biochemical
reactions.
Quantitaive estimation of enzymes, substrates or inhibitors
can be done(Enzyme assays)
Finds its applications in various fields such as Cancer
therapy, weed control etc.

24. References
1. David L. Nelson and Michael M. Cox, Lehninger Principles
of Biochemistry, 4th edition, W.H. Freeman & Co., New
York.
2. Taiz, L., and Zeiger, E. 1998. Plant Physiology. Sinaur
Associates Inc. Publishers, Sunderland Massachusetts.
3. Pranav kumar and Usha Mina, 2015, Life Sciences-
Fundamentals and Practice –I, 4th edition, Pathfinder
publications, New Delhi.
4. https://www.tamu.edu/faculty/kunkel/41096exam2.html