Ans: c (Hydrolysis) Ref: KDT, 6 ed, p.25, 345; Harper 27 ed, p.96The final common pathway in the metabolism of all the three involves hydrolysis by an esterase.The cleavage of a drug molecule by taking up a water molecule; occurs in liver, intestine, plasma and other tissues.E.g.: choline esters, lignocaine, procaine, procainamide, pethidine, oxytocin, atracurium, mivacurium.Atracurium:1) Usually inactivated by spontaneous nonenzymatic degradation (Hoffman elimination)2) One small fraction is eliminated by hydrolysis by cholinesterase.Mivacurium:Shortest acting competitive blocker, rapidly metabolised by plasma cholinesterases.Succinvlcholine:Shortest acting depolarizing muscle relaxant which is hydrolysed by plasma pseudocholinesterase to succinyl monocholine and then succinic acid and choline.Action lasts only for 3-5 min. It causes phase 2 blockade.Classification of enzymes:A. Oxidoreductases:i) Dehydrogenases- removes hydrogen by coenzymes.ii) Oxidases- remove H2 and form H2O2.iii) Reductases-iv) Peroxidases-v) Catalasesvi) Oxygenase-monooxygenasedioxygenaseB. Transferases:Transfer one group from substrate to another.TransketolaseTransaldolaseKinases (transfer phosphate group from ATP to substrate)TransaminasePhosphorylaseC. Hydrolases:Cleavage of a molecule by taking up a water molecule1. Phosphatase2. Glycosidases3. EsterasesD. Lyases:Add or remove small molecules like water,ammonia, CO2e.g.:1) decarboxylase2) synthases- ALA synthase.3) aldolase4) fumaraseE. Isomerases:i) Epimerasesii) Mutasesiii) RacemasesF. Ligases:1. Ligation of two molecules at the expense of high energy phosphate bond. eg:synthetases2. CarboxylasesRemember:Carboxylases are ligases but decarboxylases are lyases.Synthetases are ligases but synthases are lyases