For Medical, Non Medical & Allied Health Science students

1. E-02: FACTORS AFFECTING
ENZYME ACTIVITY
By
Santhosh Kumar. N M.Sc., PhD,(Medical)
Assistant Professor
Department of Biochemistry
SIMS & RH

2. Various factors which affect enzyme activity
– Substrate concentration
– Enzyme concentration
– Product concentration
– Temperature
– Hydrogen ion concentration (pH)
– Presence of inhibitors

3. EFFECT OF SUBSTRATE
CONCENTRATION
Increase in [S], 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.

4. 3. Phases:
1. At low [S], the velocity of reaction is directly proportional to the
substrate level.
2. In second phase, [S] is not directly proportional to the enzyme activity.
3. The reaction is independent of the substrate concentration

5. 5
Michaelis – Menten Equation
It describes how reaction velocity varies with [S]
K1 K3
E + S ES P + E
K2
[K1, K2 and K3 are rate constants,
“S” is Substrate,
“E” is Enzyme,
“ES” is Enzyme substrate complex & “P” is Product]

6. 6
Reaction velocity varies with substrate concentration.
Vmax [S]
V =
Km + [S]
V = Initial reaction velocity
V max = Maximal Velocity
Km = Michaelis Menten constant (K2 + K3)/ K1
[S] = Substrate concentration

7. 7
Measured velocity V = I/2 Vmax
Vmax [S]
1/2 Vmax =
Km + [S]
Vmax 2[S]
Km + [S] =
Vmax
Km + [S] = 2[S]
Km = 2[S] - [S]
Km = [S]
If Km is set equal to [S] at which the
velocity is half maximal.
V = ½ Vmax

8. Significance of Km
• thus Km provides a measure the [S] required for significant catalysis to
occur
• - Km is not a true dissociation constant, but it does provide a measure of
the affinity of an enzyme for its substrate in the ES complex
– High Km : weak binding with its substrate
– Low Km : strong binding
• Vmax of a reaction is an index of the catalytic efficiency of an enzyme
• It is useful in comparing the activity of one enzyme with that of another

9. Rate of reaction or velocity is directly
proportional to the concentration of
enzyme, when sufficient substrate is
present
EFFECT OF
ENZYME CONCENTRATION

10. EFFECT OF
TEMPERATURE
Velocity of an enzyme reaction increases with
increase in temperature up to a maximum and then
declines.
A bell-shaped curve is observed.
Human enzyme have the optimum temp around 370C.
Ex: Venom phosphokinases & Taq polymerase are
active even at 1000C
Urease have optimum activity around 600C
Temp at which maximum amount of
The ‘S’is converted to the Product
per unit time -optimum temp

11. EFFECT OF
PH
-Each enzyme has an optimum pH at which the
velocity is maximum.
-Graph will show a bell-shaped curve.
Example:
Most enzymes show optimum activity between pH
(6 & 8)
Pepsin (pH 1-2)
Acid phosphatase (pH 4-5)
Alkaline phosphatase (pH 9-10).

12. Effect of
Product Concentration
Accumulation of reaction products generally decreases the enzyme velocity.
Heme (ALA synthase) and
Cholesterol (HMG CoA-reductase)

13. IF YOU believe
IN
yourself
anything Is Possible
ThankYou
Next Class E-04: Enzyme Inhibition & Its Clinical Importance