Characterization of P-S bond hydrolysis in organophosphorothioate pesticides by organophosphorus hydrolase.
The extensive use of organophosphorothioate insecticides in agriculture has resulted in the risk of environmental contamination with a variety of broadly based neurotoxins that inhibit the acetylcholinesterases of many different animal species. Organophosphorus hydrolase (OPH, EC 3.1.8.1) is a broad-spectrum phosphotriesterase that is capable of detoxifying a variety of organophosphorus neurotoxins by hydrolyzing various phosphorus-ester bonds (P-O, P-F, P-CN, and P-S) between the phosphorus center and an electrophilic leaving group. OPH is capable of hydrolyzing the P-X bond of various organophosphorus compounds at quite different catalytic rates: P-O bonds (kcat = 67-5000 s-1), P-F bonds (kcat = 0.01-500 s-1), and P-S bonds (kcat = 0.0067 to 167 s-1). P-S bond cleavage was readily demonstrated and characterized in these studies by quantifying the released free thiol groups using 5,5'-dithio-bis-2-nitrobenzoic acid or by monitoring an upfield shift of approximately 31 ppm by 31P NMR. A decrease in the toxicity of hydrolyzed products was demonstrated by directly quantifying the loss of inhibition of acetylcholinesterase activity. Phosphorothiolate esters, such as demeton-S, provided noncompetitive inhibition for paraoxon (a P-O triester) hydrolysis, suggesting that the binding of these two different classes of substrates was not identical.
Lai
K
K
Department of Biochemistry and Biophysics, Texas A&M University, College Station 77843, USA.
Stolowich
N J
NJ
Wild
J R
JR
D043303:Aryldialkylphosphatase; D001387:Azinphosmethyl / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D001673:Biodegradation, Environmental; D004222:Disulfoton / Q000737:chemistry / Q000378:metabolism; D004785:Environmental Pollutants / Q000378:metabolism; D004950:Esterases / Q000378:metabolism*; D005417:Flavobacterium / Q000201:enzymology; D006868:Hydrolysis; D007306:Insecticides / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008294:Malathion / Q000737:chemistry / Q000378:metabolism; D015394:Molecular Structure; D009946:Organothiophosphorus Compounds / Q000737:chemistry / Q000378:metabolism; D010261:Paraoxon / Q000378:metabolism; D063088:Phosphoramides; D011549:Pseudomonas / Q000201:enzymology; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity
D004785:Environmental Pollutants; D007306:Insecticides; D009946:Organothiophosphorus Compounds; D063088:Phosphoramides; D011994:Recombinant Proteins; C012762:azinphos ethyl; D001387:Azinphosmethyl; D004222:Disulfoton; C001969:acephate; C003117:phosalone; D004950:Esterases; D043303:Aryldialkylphosphatase; D010261:Paraoxon; D008294:Malathion