(b) The catalytic reaction occurs while the two are bonded together in the enzyme-substrate complex.
ii. Induced-Fit Theory:
- It is modification of lock and key hypothesis which was proposed by Koshland in 1959. According to this
theory the active site of the enzyme contains two groups, buttressing and catalytic. The buttressing group
is meant for supporting the substrate. The catalytic group is able to weaken the bonds of reactants by
electrophilic and nucleophilic forces. - The two groups are normally at a distance. As soon as the substrate comes in contact with the buttressing
group, the active site of the enzyme undergoes conformational changes so as to bring the catalytic group
opposite the substrate bonds to be broken. - Catalytic group helps in bringing about chemical reaction. The substrate is converted into product. The
product is unable to hold on the buttressing site due to change in its structure and bonds. Buttressing group
reverts to its original position. The product is released.
Features:
(1) Active site is not rigid and pre-shaped.
(2) The interaction of the substrate with the enzyme induces a conformation change in enzyme.
Fig: Induced Fit Model
Unit of Enzyme:
- The International Commission on Enzymes
established by International Union of
Biochemistry (IUB) defines, One International
Unit of enzyme as the amount of enzyme that
catalyses the formation of one micromole of
product in one minute. In determining the One
International Unit the conditions of assay must
be specified because enzymes are very sensitive
to factors such as pH, temperature, and ionic
strength. - Another definition for units of enzyme is the
‘katal’.
Properties of Enzyme and Factors Influencing
Enzyme Activities:- The properties and characteristics of enzymes are
given in table. - Enzyme reaction rates are influenced by
several factors such as pH, temperature and the
concentration of reactants.