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TITLE : Bisubstrate Reactions
Presented by
Dilruba Afrin
Course : GEB-407
Dept. of Genetic Engineering & Biotechnology
University of Rajshahi
Contents
Bisubstrate Reactions sequential or single-
displacement reactions Ordered sequential
reactions Random sequential
reactions ping-pong or double-
displacement reactions
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
Bisubstrate Reactions
Bisubstrate Reactions
Sequential or single
displacement
Ordered Random
Ping-pong or double
displacement
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
sequential or single-displacement
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.
1.Ordered sequential reactions
sequential or single-displacement
reactions
This is another view of ordered sequential.
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 & Qare the products).
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.
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.
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.
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
ping-pong or double displacementreactions
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.
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.
ping-pong or double displacement
reactions
THANKS TO ALL
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