bisubstrate reactions enzyme kinetics

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

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Page 1: Bisubstrate reactions enzyme kinetics

TITLE : Bisubstrate Reactions

Presented by

Dilruba Afrin

Course : GEB-407

Dept. of Genetic Engineering & Biotechnology

University of Rajshahi

Page 2: Bisubstrate reactions enzyme kinetics

Contents

Bisubstrate Reactions sequential or single-

displacement reactions Ordered sequential

reactions Random sequential

reactions ping-pong or double-

displacement reactions

Page 3: Bisubstrate reactions enzyme kinetics

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.

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Page 4: Bisubstrate reactions enzyme kinetics

Bisubstrate Reactions

Bisubstrate Reactions

Sequential or single

displacement

Ordered Random

Ping-pong or double

displacement

Page 5: Bisubstrate reactions enzyme kinetics

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

Page 6: Bisubstrate reactions enzyme kinetics

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

Page 7: Bisubstrate reactions enzyme kinetics

sequential or single-displacement

reactions

This is another view of ordered sequential.

Page 8: Bisubstrate reactions enzyme kinetics

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).

Page 9: Bisubstrate reactions enzyme kinetics

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.

Page 10: Bisubstrate reactions enzyme kinetics

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.

Page 11: Bisubstrate reactions enzyme kinetics

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.

Page 12: Bisubstrate reactions enzyme kinetics

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

Page 13: Bisubstrate reactions enzyme kinetics

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.

Page 14: Bisubstrate reactions enzyme kinetics

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

Page 15: Bisubstrate reactions enzyme kinetics

THANKS TO ALL