The document discusses factors that influence enzymatic reactions, including pH, temperature, and substrate concentration. It states that enzymes have an optimum pH and temperature at which their activity is highest. Both higher and lower pH and temperatures can decrease enzyme activity or even denature the enzyme. The initial reaction rate increases with substrate concentration until the enzyme reaches saturation, at which point further increases in substrate have no effect. The Michaelis-Menten theory postulates that at low substrate concentrations the reaction rate is not at its maximum velocity due to lack of enzyme saturation.

1. Factors Influencing Enzymic
Reactions
Dr.Geeta Jaiswal

2. Effect of pH
Most Enzymes have characteristic pH
at which their activity is maximum
Above and below that pH, the enzyme
activity decreases
If a curve is drawn between Enzyme
activity and pH on a given substrate
concentration maximum activity is
revealed at a definite pH – known as
Optimum pH

4. Suitable ionic formation is
controlled by pH
At low pH proteins are protonated
and the structure is destroyed or
substrate may not be in the right
ionic form
High pH may denature the
protein molecule

5. Effect of Temperature
 Each Enzyme is most active at a
particular temperature.
Starting with zero the kinetic energy
of molecules increases with the rise in
temperature.
More molecules collide and undergo
a reaction

7. After crossing the optimum temperature
enzyme activity declines since the bonds
in the protein molecules are disrupted.
At times high temperature results in
denaturation of the enzyme molecule.
For most enzymes optimum temperature
lies between 35o
to 400
C
At low temperatures enzyme reaction
requires more time.

8. Effect of Substrate Concentration
The initial velocity of an enzyme catalyzed
reaction is proportional to the substrate
concentration.
With the rise of substrate concentration
the enzyme activity increases up to a
certain point.
After this point a further increase in
substrate concentration has no effect,
since the enzyme is fully saturated.

11. Michaelis Menten’s theory
It was Michaelis Menten who suggested
an explanation to these findings
He postulated that :- At low substrate
concentrations the enzyme is not
saturated with the substrate and the
reaction is not proceeding at maximum
velocity.
When enzyme is saturated with the
substrate max velocity is observed.

13. Maximum Velocity or Vmax
When the enzyme is fully saturated with
the substrate Maximum Velocity of an
enzymic reaction is observed denoted as
Vmax
The substrate concentration at which the
velocity is half the maximum is called
Michaelis Constant and is termed as Km

14. Km and affinity of Substrate
Km indicates the affinity of the substrate
towards the enzyme and is inversely
proportional to the affinity.
 Km α 1
affinity
 Higher affinity smaller Km
 Lower affinity higher Km

16. The Michaelis Menten’s is given by
the expression
Vmax [S] + [S]
V0 =
Km + [S]
OR
Vmax [S]
V0 =
[S] + Km

17. Importance of Km
Km is the concentration of substrate at
which half of the active sites are filled , so
half maximum velocity.
It indicates the degree of affinity of an
enzymes for a particular substrate.
The more the Km the less the affinity of
enzyme for substrate

18. Km is neither influenced by enzyme
concentration nor by non-competetive
inhibitors .
It is altered completely by competitive
inhibitors; allosteric modulators, pH
temperature and substrate concentration.
Determination of important physical
constants of an enzyme such as Vmax and
Km are difficult from a curve that would be
obtained by plotting [ v ] and [ s ]

19. Determination of important physical
constants of an enzyme such as Vmax and km
are difficult from a curve that would be
obtained by plotting [v] and [s]

20.  So the Michaelis Menten equation can be
transformed into the form which is useful
in plotting experimental data
This equation is called Line weaver Burk
and is an equation for a straight line
Y=mx + c

1 1 Km. 1
= + .
v Vmax Vmax [s]

21. Double Reciprocals or LineWeaverBurks
Plot
When 1/v0 is plotted against 1/[s] ,a
straight line is obtained
Slope of which is Km / Vmax
Intercept of 1/Vmax on Y axis
Intercept of 1/Km on X axis

22. Slope = Km/Vmax
1/Vmax
-1/ Km
• M=slope of straight line
• C=Intercept on Y axis
• X=Intercept on X axis

23. Thank - You