Protein Aryldialkylphosphatase

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1 protein

1.1 structure
1.2 catalysis
1.3 kinetics





protein
structure

phosphotriesterase (pte) belongs family metalloenzymes has 2 catalytic zn metal atoms, bridged via common ligand , coordinated imidazole side chains of histidine residues clustered around metal atoms. protein forms homodimer. overall structure consists of α/β-barrel motif, present in other 20 catalytic proteins. active sites of these proteins located @ c-terminal portion of β-barrel, active site of pte located.



reaction schematic of enzyme-catalyzed hydrolysis of paraoxon diethyl phosphoric acid , p-nitrophenol. 


catalysis

catalysis of organophosphates occurs via nucleophilic substitution inversion of configuration (sn2 mechanism) phosphorus centre of substrate. in active site, metal cations aid in catalysis further polarizing p–o bond of substrate, makes more susceptible nucleophilic attack. furthermore, basic residue abstracts proton water molecule, , hydroxide ion produced bridges 2 divalent cations , acts nucleophile. oh attacks phosphorus centre of substrate, followed proton transfer event. p–o bond broken, , products released active site. turnover rate (kcat) of phosphotriesterase 10 s hydrolysis of paraoxon, , products p-nitrophenol , diethyl phosphoric acid.



kinetics

the kinetic model proposed consists of reversible binding step takes place between enzyme , substrate, , formation of michaelis complex (es). irreversible step follows, when p–o bond cleaved , transient enzyme + product (ep) complex formed. lastly, products released , free enzyme (e) regenerated.








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