Enzyme Inhibition and Drug Action

Transcription

1 Enzyme Inhibition and Drug Action Malfunction of enzyme Introduction of enzyme by microorganism Disease Inhibition of enzyme - Interesting but difficult drug strategy Inhib. of enzymes from microorganisms - Enzyme only in microorg. - Different structure of enzyme, human and microorg Antibact. sulfonamide 2 S 2 2 ABA Dehydropteridinsyre 2 Tetrahydrofolic acid C 2 C 2 Folatreduktase Trimetoprim 2 2 Dehydrofolic acid C 2 Folic acid From food igher animals C 2 C 2 C 2 2 Essintial processes, animals and bacteria C 3 2 C 3 C 3 Enzyme inhibition k k 3 E + S [ E-S ] [ E- ] E + k 2 E: Enzyme S: Substrate : roduct Two last steps!irreversible, E-S to E- rate limiting eaction velocity, =k 3 [E-S] ate of form. ES: k [E] ate of decomp. ES: (k + k 3 )[E] Assume steady state ([E-S] doesn t change) k [E] = (k + k 3 )[E] [E] (k 2 + k 3 ) / k Michaelis const.: = (k 2 + k 3 ) / k [E] [E] = [E tot ] - [E-S] ([E tot] - [E-S] [E tot ] +

2 k k 3 E + S [ E-S ] [ E- ] E + k 2 E: Enzyme S: Substrate : roduct [E tot ] + =k 3 [E-S] = k 3 [E tot ] + : All enzyme sites occupied by S >>, +! =k 3 [E tot ] = + Michaelis Menten eq. : 2 = + Michaelis Menten eq. : 2 = + Lineweaver-Burk eq. Slope = Measure rate at different : Determine and -

3 eversible and irreversible enzyme inhibitors E + [ E-I ] E + [ E-I ] eversible inhibition Competitive on-competitive If covalently bond to enzyme, bond relatively easily be broken i.e. hydrol. of ester E + S [ E-S ] E + I [ E-I ] With inhibitor o inhib. Binding to the same site Inhib. can be reversed by increasing unchanged increase - Slope = Structural resemblance S and I Designed I drugs - Antimetabolites Ex. antimetabolites 2 Antibact. sulfonamide 2 S 2 2 From food igher animals C 2 C 2 Folic acid ABA Dehydropteridinsyre Essintial processes, animals and bacteria 2 C 2 C 2 Me I everse transcriptase A chain Me AZT Thymidin

4 Ex. transition state analogs 2 Adenosine deaminase 2 Also metab. of anticancer / antiviral adenine deriv. Adenine Inosine sp 3 Coformycin eversible inhibition Competitive on-competitive E + S [ E-S ] + I [E-S-I] E + I [ E-I ] + S Binding to different sites Inhib. can be reversed by increasing decrease unchanged - With inhibitor o inhib. Slope = Inhib. and substrate very different structures Difficult to design inhib.

5 Irreversible enzyme inhibitors E + [ E-I ] ften covalent bonds between E and I Enzyme is permanently modified and inactivated Affinity labels and active site directed irreversible inhibitors Mechanism based irreversible enzyme inactivators Structural recemblance with substrate Electrophilic - alkylate nucleophilic subst in enzyme active site Low selectivity - generally highly toxic From last chapter Binding of ligand to receptor Covalent bond Ionic bond ydrogen bond ydrophobic interaction Covalent bond strong; kcal/mol, ormally irreversible bonding ex. Acetylcholine esterase (enzyme) inhibitors Acetylkolin () Acetylkolin-esterase Kolin Acyltransferase Kolin (Ch) erve cell Synapse Effector celle erve potensial reseptor Ch-acetyltransferase Ch (exess) -esterase Ch

6 eversible inhibitors k 3 () Inhibitor Me 2 k 3 (inhibitor) Me 2 Me 2 More difficult to cleave eversible inhibitor (drugs): k 3 (inhib) < k 3 () eostigmin yridostigmin Myastenia gravis (weak muscles, reduced sensitivity to Acetylcholine) Irreversible Inhibitors Gen structur mustard gasses L 2 L: Leaving group : alkoksy 2: alkyl, alkoksy, amino Tabun F Sarin ot drugs, nerve gasses, insecticides etc. Malation not tox. S S only insects Malaoxon S Act as mustard gasses Aging ralidoxim L 2 L Me ralidoxim motgift Me

7 Affinity labels and active site directed irreversible inhibitors Mechanism based irreversible enzyme inactivators Suicide substrate - kcat inhibitors - Trojan horse inhib. - latent alkylating agent! ro-drug, must be activated by the enzyme enicillins are cleaved by!-lactamase S!-Lactamase S Clavulanic acid irreversibly inhibits!-lactamase u u u u