Dr.S.Karthikumar Asst. Prof., Dept. of Biotechnology Kamaraj College of Engineering and Technology S.P.G.C.Nagar, Virudhunagar, Tamilnadu, India

1. Effect of pH and Temperature on
Enzyme Activity
Dr.S.Karthikumar
Asst. Prof., Dept. of Biotechnology
Kamaraj College of Engineering and Technology
S.P.G.C.Nagar, Virudhunagar, Tamilnadu, India

2. • Each enzyme has an optimum pH at which it works best
• Trypsin and Pepsin are both enzymes in the digestive system which
break protein chains in the food into smaller bits
• Pepsin works in the highly acidic conditions of the stomach. It has an
optimum pH of about 1.5.
• Trypsin works in the small intestine, which have optimum pH of around 8.0
• pH affect the structure of an enzyme molecule, and the sorts of
bonds that it may form with its substrate

3. If a enzyme has an optimum pH around 7, and
reaction mixture pH is also around 7

4. If pH is more acidic
at a lower pH - in other words under acidic conditions. It won't affect the -NH3
+ group, but the -
COO- will pick up a hydrogen ion
no longer have the ability to form ionic bonds between the substrate and the enzyme

5. If pH is more alkali
the -COO-group won't be affected, but the -NH3
+ group will lose a hydrogen ion

6. • The rates of enzyme-catalysed
reactions vary with pH
• The pH at which the rate is a
maximum is called the pH
optimum
• the plot of rate against pH is
called a pH profile

7. Reaction scheme considering the binding of substrate to the protonated and unprotonated enzyme
Rate limiting step is the dissociation of ES complex (Low Kcat)
Proton transfer is more rapid than that of any other chemical group
4 equilibrium constants = KS, KE, KES, KS’

8. • All the 4 equilibrium constants are not independent but are related
KE x KS’ = KES x KS
• If KE = KES then KS’ = KS
There is no difference in the substrate binding between protonated and
unprotonated enzyme
• If KE ǂ KES
• 𝑣 =
𝑣 𝑚𝑎𝑥 𝑆
𝐾𝑠
1+ 𝐻+
𝐾 𝐸
+ 𝑆
1+ 𝐻+
𝐾 𝐸𝑆

10. Effect of Temperature on Enzyme Activity
• For molecules to react, they have to collide with an energy equal to or greater than
the activation energy for the reaction
• Heating a reaction makes the molecules move faster and so collide more often.
More collisions in a given time means a faster reaction.
• Heating an enzyme gives the protein chains extra energy and makes them move
more. If they move enough, then the bonds holding the tertiary structure in place
will come under increasing strain.
• Hence, reaction temperature influences the Reaction Rate
• But above certain point of temperature there is a dramatic fall in reaction rate.
• At higher temperature, the weaker bonds will break first - van der Waals attractions
between side groups, and then hydrogen bonds. As soon as these bonds holding the
tertiary structure together are broken, then the shape of the active site is likely to
be lost.

11. • The temperature at which the rate
is fastest is called the optimum
temperature for that enzyme.
• Different enzymes have different
optimum temperatures.
• The optimum temperature for a
particular enzyme varies depending
on how long it is exposed to the
higher temperatures

12. • Arrhenius equation is the starting point to relate temperature and
reaction rate

15. THANK YOU