2. BISUBSTRATE REACTION
• When an enzyme catalyzing a reaction involving two
substrates and yields two products it is called as
bisubstrate reaction.
• Approximately 60% reaction accounts for biochemical
reaction.
A + B P + Q
3. • It is either transferase reaction in which the enzyme catalyzes the
transfer of a specific functional group, from one of the substrate to
the other.
P-X + B P + B-X
• Bisubstrate reaction is a oxidation reduction reaction in which
reducing equivalents are transferred between the two substrates.
4. Example:
Hydrolysis of peptide bond by trypsin is the transfer of
the peptide carbonyl group from the peptide nitrogen
atom to water.
5. • W. Cleland introduced a nomenclature system for representing
enzymatic reaction:
• Substrate is represented by A, B, C and D.
• Products is represented by P. Q, R and S.
• Stable enzymes forms are designated by E, F and G.
• The number of reactants and products in a given reaction are specified in
order, by Uni (one), Bi (two), Ter (three) and Quad (four).
The reaction that requires two substrate and yield two products that
is Bi Bi reactions.
6. TYPES OF BI BI REACTION
• They are of two major types namely:
1. SEQUENTIAL REACTIONS:
oAll the substrates involved are bound to the enzyme before
catalysis of the reaction takes place to release the products.
oIt is also called Single Displacement reactions.
oBoth substrate and enzymes forms ternary complex.
oIt is sub-classified into two types: ordered sequential reaction
and random sequential reaction
7. ORDERED SEQUENTIAL REACTION
• All the substrates are bound to the enzyme in a defined order or
sequence. The products too, are released after catalysis in a
defined order or sequence.
8. • Example : lactate dehydrogenase enzyme catalyzes glucose
metabolism.
9. RANDOM SEQUENTIAL REACTION
• The substrate and products are bound and then released in no
preferred order or ‘random’ order.
10. Example:
Creatine kinase enzyme which catalyzes the substrate
creatine and ATP ,to form the products, phosphocreatine and ADP.
11. 2. PING PONG REACTION:
• Mechanism in which one or more products are released before
all substrates have been added are known as Ping Pong
reaction.
• Also called as Double Displacement reaction.
• It is characterized by the change of the enzyme into an
intermediate form when the first substrate to product reaction
occurs.
12. • This indicates temporary and the enzyme must be found in its
original form at the end of the reaction.
13. Example: The enzyme aspartate amino transferase catalyzes the
transfer of an amino group from aspartate to alpha ketoglutarate.
14. REFERENCE
• Voet Donald and Voet Judith, ‘Biochemistry’, second
edition;1995, Pg. 362-363.
• Garett Regnard and Grisham Charles, ‘Biochemistry’, second
edition; 1999, Pg. 448-454.
