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A Handbook of Biology
Ç) PRËSËÑÇË ØF ÏÑHÏBÏTØR
The binding of specific chemicals (inhibitor) shuts off the enzyme activity.
This is called inhibition.
The inhibitor is closely similar to the substrate in its molecular structure
and is called as competitive inhibitor. It competes with the substrate for
the binding site of the enzyme. As a result, the substrate cannot bind and
the enzyme action declines.
(AIPMT 2005)
E.g. Malonate is similar to the substrate succinate. So, it inhibits succinic
dehydrogenase in the following reaction.
(NEET 2020)
Succinate
Fumarate
Succinic dehydrogenase
Competitive inhibitors are used to control bacterial pathogens.
ÇLÅSSÏFÏÇÅTÏØÑ ÅÑD ÑØMËÑÇLÅTÜRË ØF ËÑZÝMËS
Oxido-reductases /
Dehydrogenases: Catalyze
oxido- reduction b/w two
substrates.
S reduced + S’ oxidized ®
S oxidized + S’ reduced
Transferases: Catalyze
transfer of a group, G (other
than hydrogen) between a
pair of substrate S and S'.
S-G + S’ ® S’-G +S
Hydrolases: Catalyze hydrolysis
of ester, ether, peptide,
glycosidic, C-C, C-halide or P-N
bonds.
Lyases:
Catalyze
removal
of
groups
from
substrate
by mechanisms other than
hydrolysis leaving double bonds.
C – C ® X – Y + C = C
| |
X Y
Isomerases: Catalyze
inter-conversion of optical,
geometric or positional
isomers.
Ligases: Catalyze the linking
of 2 compounds together. E.g.
enzymes catalyzing joining of
bonds like C-O, C-S, C- N, P-O
etc.