bisubstrate reactions enzyme kinetics

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Bisubstrate Reactions

TITLE : Bisubstrate Reactions

Presented byDilruba AfrinCourse : GEB-407Dept. of Genetic Engineering & BiotechnologyUniversity of Rajshahi

ContentsBisubstrate Reactions sequential or single-displacement reactionsOrdered sequential reactionsRandom sequential reactionsping-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.


Bisubstrate Reactions1.sequential or single-displacement reactionsSequential 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 reactionsRandom 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 reactionssequential or single-displacement reactionsThis is another view of ordered sequential.

sequential or single-displacement reactions2.Random sequential reactionsWhere 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).

sequential or single-displacement reactionsAn 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 reactionsGroup 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 displacement reactionsAn example of a ping-pong reaction

Reactions that shuttle amino groups between amino acids and -keto acids are classic examples of double-displacement mechanisms.The enzyme aspartate aminotransferase catalyzes the transfer of an amino group from aspartate to -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, -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 reactionsTHANKS TO ALL


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