|Type of Inhibition||Effect on Maximum Reaction Velocity(Vmax)||Effect on Km(Affinity of Enzyme for its substrate)||Reversible/ Irreversible||Examples|
|Competitive Inhibition (Inhibitor- a structural Analogue).
There is a competition between substrate and the inhibitor for the active site
|Unchanged||Increased||Reversible||1) HMG Co A Reductase- inhibited by Statins- used as cholesterol lowering drugs. 2) Epoxide Reductase – inhibited by Dicoumarol- used as an anticoagulant.
3) Dihydrofolate Reductase-inhibited by Methotrexate- used as anticancer drug.
4) Pteroyl Synthase- inhibited by PABA (Para- amino –benzoic –acid) used as antibiotic.
5) Angiotensin convertase enzyme Inhibitor- inhibited by Captopril –used as an antihypertensive drug.
6) Succinate dehydrogenase- inhibited by Malonate acts as a poison.
7) Lactate dehydrogenase- inhibited by Oxamate- acts as a poison.
|Non competitive (Inhibitor binds at a site other than the active site)||Decreased||Unchanged||Can be reversible or irreversible||1) Enolase is inhibited by Fluoride used for sample collection for glucose estimation. 2) PDH complex, Alpha ketoglutarate dehydrogenase complex, glyceraldehyde-3-P dehydrogenase(-SH group containing enzymes) are inhibited by Arsenate, Acts as a slow poison
3) Cytochrome oxidase- Inhibited by cyanide acts as a poison.
4)Cyclooxygenase is inhibited by Aspirin-used as an anti inflammatory, analgesic and antipyretic drug (Inhibits formation of prostaglandins)
|Suicidal inhibition, Also called Mechanism based inhibition
Inhibitor gets activated by host enzyme to inhibit the subsequent enzyme
|Decreased||Increased||Irreversible||1)Inhibition of Xanthine oxidase by Allopurinol, used for the treatment of gout. 2) Inhibition of Aconitase by fluoroacetate- used as a rat poison
3) Inhibition of Transpeptidase by Penicillin- used as an antibiotic
4) Inhibition of Ornithine decarboxylase by Di fluoro methyl ornithine(DFMO)
5) Mono Amine Oxidase is inhibited by Deprenyl used to treat Parkinson disease and depression.
|Allosteric Inhibition (Binding of the inhibitor alters either the affinity of the enzyme for its substrate or the reaction velocity is decreased||V max is decreased in V type enzymes||Km is increased in K type enzymes||Reversible||Most of them are physiological inhibitors. 1)ATP and Citrate are allosteric inhibitors of PFK-1
2) Fr 2,6 bisphosphate is an allosteric inhibitor of Fr1,6 bisphosphatase enzyme.
|Feed back inhibition, also called Product inhibition The product of the reaction pathway inhibits the key regulatory enzyme.||Decreased||constant||Reversible depending upon the need of the product||1) Inhibition of HMG Co A Reductase by Mevalonate(Immediate product) and cholesterol(Final product) 2) Inhibition of Aspartate transcarbamoylase
by UTP and CTP, the products of this pathway.
|Un competitive inhibition Inhibitor binds to the enzyme substrate complex||Decreased||Decreased||Ir- reversible||Inhibition of placental alkaline phosphatase by Phenyl Alanine|
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