Aryldialkylphosphatase

Aryldialkylphosphatase (EC 3.1.8.1, also known as phosphotriesterase, organophosphate hydrolase, parathion hydrolase, paraoxonase, and parathion aryl esterase; systematic name aryltriphosphate dialkylphosphohydrolase) is a metalloenzyme that hydrolyzes the triester linkage[1] found in organophosphate insecticides: 1jgmA:44-359 1ez2A:44-359 1dpmA:44-359 1pscA:44-359 1eywA:44-359 1hzyB:44-359 1qw7A:44-359 1pta :44-359 1p6cA:44-359 1p6bA:44-359 2d2hA:43-358 2d2jA:43-358 The gene (opd, for organophosphate-degrading) that codes for the enzyme is found in a large plasmid (pSC1, 51Kb) endogenous to Pseudomonas diminuta,[2] although the gene has also been found in many other bacterial species such as Flavobacterium sp.

[3] Bacterial isolates capable of degrading organophosphate (OP) pesticides have been identified from soil samples from different parts of the world.

[3][4] The first organophosphate-degrading bacterial species was isolated from a soil sample from the Philippines in 1973,[5] which identified as Flavobacterium sp.

[7] Catalysis of organophosphates occurs via a nucleophilic substitution with inversion of configuration (SN2 mechanism) about the phosphorus centre of the substrate.

[7] In the active site, the metal cations aid in catalysis by further polarizing the P–O bond of the substrate, which makes it more susceptible to a nucleophilic attack.

Furthermore, a basic residue abstracts a proton from a water molecule, and the hydroxide ion produced bridges the two divalent cations and acts as the nucleophile.

[9] The turnover rate (kcat) of phosphotriesterase is nearly 104 s−1 for the hydrolysis of paraoxon,[10] and the products are p-nitrophenol and diethyl phosphoric acid.

[3] It does not seem to have a natural occurring substrate and may thus have optimally evolved for utilizing paraoxon and other common agricultural pesticides.

[7] Its wide substrate specificity and catalytic efficiency makes it an attractive target for the potential use of microbes containing the opd gene in detoxifying soils that are toxic due to pesticide overuse.

[3][17] As a result, the use of organophosphate-degrading microorganisms is a potentially effective, low-cost, and environmentally friendly method of removing these toxic compounds from the environment.

[3] Bacterial species that had the ability to degrade organophosphate pesticides have been isolated from soil samples from different parts of the world.

Reaction schematic of enzyme-catalyzed hydrolysis of paraoxon into diethyl phosphoric acid and p -nitrophenol.
Schematic diagram of cell wall of Gram-negative bacteria (Pseudomonas) showing the inner membrane where PTE is anchored and the periplasmic space.
Organophosphate compounds that serve as substrates for enzyme-catalyzed hydrolysis by PTE.