2. Enzyme kinetics
• Enzyme kinetics is the study of the chemical reactions that are catalyzed by enzymes.
• In enzyme kinetics, the reaction rate is measured and the effects of varying the conditions of the
reaction are investigated.
• The two common kinetic processes are Michaelis plot and Line weaver Burke plot.
3. Michaelis- Menten plot:
1. In biochemistry, Michaelis–Menten kinetics is one of the best-known models of enzyme kinetics. It
is named after German biochemist Leonor Michaelis and Canadian physician Maud Menten.
2. In 1913, they proposed a mathematical model of the reaction. It involves an enzyme, E, binding to
a substrate, S, to form a complex, ES, which in turn releases a product, P, regenerating the original
enzyme.
This may be represented schematically as
4. 3. The model takes the form of an equation describing the rate of enzymatic reactions, by relating
reaction rate (rate of formation of product, [P] ) to the concentration of a substrate [S]. Its formula
is given by
4.
5. This equation is called the Michaelis–Menten equation. Where
a) =d[P]/dt = rate of formation of product
b) [P] = Molar concentration of product formed
c) [S]= Molar concentration of substrate (reactant) used.
d) Kcat = catalytic rate constant
e) Vmax = maximum rate achieved by the system at high substrate concentration
f) Km = Michaelis constant which is numerically equal to the substrate concentration at which the reaction rate
is half of Vmax.
g) [Eo] = initial concentration of enzyme
5. 6. On the bases of above equation Michaelis Menten graph has been plotted between Substrate concentration
[S] and initial reaction velocity (Vo)
6. • The three mean observation of Michaels Menten plot are as shown below
a) Substrate concentration [S] is less then reaction rate (V) is directory propositional to substrate concentration
[S]. It is an example of first order reaction.
b) when [S]>>> Km then V does note depend on [S]. It is an example of zero order kinetics.
c) when [S]= Km then Initial velocity (Vo) of reaction become half of max velocity (Vmax)
7. Significance
a) The equation explains the velocity of enzyme reaction.
b) Vmax provides the theoretical information about possible maximum rate of reaction and can use as
an indicator to detect catalytic efficiency.
c) Km (Dissociation constant for [ES]) explain binding effect (relative stability); greater the Km
value, lesser the binding of substrate to the enzyme.
d) If Vmax/Km has high value than A strong affinity between the enzyme and substrate has been
possible.
8. Lineweaver-Burk Plot
1. It is also known as double reciprocal plot.
2. It is the graphical representation of Lineweaver-Burk of enzyme kinetics.
3. In M and M equation, When [S] increase , It is not possible to determine Vmax and Km.
4. To solve this problem Lineweaver-Burk, Modify the M & M equation as
[ ]
[ ]
[S]
9. Where
Vo =Vi= Initial rate of velocity
Km = The Michaelis constant
Vmax= maximum rate achieved by the system at high
substrate concentration.
[S]= molar concentration of substrate
Above equation can compare with the straight line
equation and draw Lineweaver-Burk plot between ; x (1/[S]) and y (1/ Vi)
y= ax + b
Where y= 1/ Vo (Vi); a = Km/ Vmax ; x= 1/[S] ; b=1/ Vmax
5. This plot shows the reciprocal of the reaction velocity (1/ Vi) as a function of substrate concentration 1/[S]in
the presence or absence of inhibitors.
6. By this plot , we can calculate Km from intercept – 1/ Km and Slope Km/ Vmax
10. Factors Affecting Enzyme Activity
Enzyme activity depends on various factors like
a) Enzyme Concentration: The correlation between enzyme concentration and velocity of reaction
is directly
proportional. On increasing enzyme concentration, velocity of the reaction also increase
b) Substrate Concentration: Rate of velocity of enzyme reaction is also directly proportional with
the concentration of substrate at the limited range.
c) Temperature: With increase temperature, velocity of enzyme reaction increase at certain level
(35-40 ℃) and above temperature it decrease.
d) Effect of pH: With increase pH, velocity of enzyme reaction increase at certain level (pH 7.4) and
above pH, it decrease.
e) Effect of activator: Certain ions like Mg+2, Zn+2 etc enhance activity.
11. Mechanism of Enzyme Action
• There are several theories by which mechanism action of an enzyme is explained.
• i) Lock and key theory: In this concept, enzymes and substrates are bind together as a lock and key fashion
12. ii) Induced fit theory:
1. In biology, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical
reaction. The active site consists of amino acid residues that form temporary bonds with the substrate (binding
site) and residues that catalyse a reaction of that substrate (catalytic site).
2. It is base on the active site of an enzyme which binds with suitable substrate and after completing suitable
effect, it breaks again.
