Bisubstrate reactions,types and mechanisms with example (Enzyme kinetics)

1. TITLE : Bisubstrate Reactions
Presented by
Dilruba Afrin
Course : GEB-407
Dept. of Genetic Engineering & Biotechnology
University of Rajshahi

2. Contents
 Bisubstrate Reactions
 sequential or single-displacement
reactions
 Ordered sequential
reactions
 Random sequential
reactions
 ping-pong or double-displacement
reactions

3. Bisubstrate Reactions
 When an enzyme catalyzing a reaction
involving two substrates and yielding two
products it is called Bisubstrate
Reactions.
 Bi-substrate reactions account for ~ 60%
of the known enzymatic reactions.
3

4. Bisubstrate Reactions
Bisubstrate Reactions
Sequential or single
displacement
Ping-pong or double
displacement
Ordered Random

5. 1.sequential or single-displacement
reactions
 Sequential reactions are one of the classes involved in
multiple substrate reactions.
 In these types of reactions ,all the substrates involved
are bound to the enzyme before catalysis of the
reaction takes place to release the products.
 In this reaction, a ternary complex of the enzyme and
both substrates forms.
 There are two types of sequential reactions-
 Ordered sequential reactions
 Random sequential reactions

6. sequential or single-displacement
reactions
1.Ordered sequential reactions
 Where a leading substrate binds first, followed by the other
substrate
 The leading substrate A binds first, followed by B. Reaction
between A and B occurs in the ternary complex and is usually
followed by an ordered release of the products, P and Q.

7. sequential or single-displacement
reactions
This is another view of ordered sequential.

8. sequential or single-displacement reactions
2.Random sequential reactions
 Where either any of the substrate may bind first followed by
the other substrate.
 In this type of sequential reaction, all possible binary enzyme-substrate
and enzyme-product complexes are formed rapidly
and reversibly when enzyme is added to a reaction mixture
containing A, B, P, and Q (here A & B are the substrates ,P & Q
are the products).

9. sequential or single-displacement reactions
An example of a random sequential reaction
 A ternary complex is still observed for this random
sequential reactions. Before catalysis, the complex includes
the enzyme, ATP and creatine. After catalysis, the complex
consists of the enzyme, ADP, and phosphocreatine.
 The overall direction of the reaction will be determined by
the relative concentrations of ATP, ADP, Cr, and CrP and the
equilibrium constant for the reaction.

10. Creatine Kinase Acts by a Random, Single-
Displacement Mechanism
Figure :
The structures of
creatine and
creatine phosphate,
guanidinium
compounds that are
important in muscle
energy metabolism.

11. 2. ping-pong or double
displacement reactions
 Group transfer reactions in which one or more
products are released before all substrates bind
the enzyme.
 The defining feature of double-displacement
reactions is the existence of a substituted
enzyme intermediate, in which the enzyme is
temporarily modified.
 In this reaction, no ternary complex is formed.

12. ping-pong reactions
Two stage reaction:
1.A functional group from 1st sub (A) is transferred to the 1st
product (P) forming a stable enzyme (E') –The Ping
2.The functional group is displaced from the enzyme by the
2nd substrate (B) to yield 2nd product (Q), regenerating the
original form of the enzyme (E) – The Pong

13. ping-pong or double displacement
reactions
An example of a ping-pong reaction
 Reactions that shuttle amino groups between amino
acids and α-keto acids are classic examples of
double-displacement mechanisms.
 The enzyme aspartate aminotransferase catalyzes
the transfer of an amino group from aspartate to α-
ketoglutarate.

14. ping-pong or double displacement
reactions
 After aspartate binds to the enzyme, the enzyme removes
aspartate's amino group to form the substituted enzyme
intermediate.
 The first product, oxaloacetate, subsequently departs. The
second substrate, α-ketoglutarate, binds to the enzyme,
accepts the amino group from the modified enzyme, and is
then released as the final product , glutamate.

15. THANKS TO ALL