Lai K, Stolowich N J, Wild J R
Department of Biochemistry and Biophysics, Texas A&M University, College Station 77843, USA.
Arch Biochem Biophys. 1995 Apr 1;318(1):59-64. doi: 10.1006/abbi.1995.1204.
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.
有机磷硫代酯杀虫剂在农业中的广泛使用导致了环境被多种具有广泛基础的神经毒素污染的风险，这些神经毒素会抑制许多不同动物物种的乙酰胆碱酯酶。有机磷水解酶（OPH，EC 3.1.8.1）是一种广谱磷酸三酯酶，能够通过水解磷中心与亲电离去基团之间的各种磷酯键（P-O、P-F、P-CN和P-S）来解毒多种有机磷神经毒素。OPH能够以截然不同的催化速率水解各种有机磷化合物的P-X键：P-O键（kcat = 67 - 5000 s-1）、P-F键（kcat = 0.01 - 500 s-1）和P-S键（kcat = 0.0067至167 s-1）。在这些研究中，通过使用5,5'-二硫代双-2-硝基苯甲酸定量释放的游离巯基，或通过31P NMR监测约31 ppm的高场位移，很容易证明并表征P-S键的裂解。通过直接定量乙酰胆碱酯酶活性抑制作用的丧失，证明了水解产物毒性的降低。硫代磷酸酯，如内吸磷-S，对对氧磷（一种P-O三酯）水解提供非竞争性抑制，这表明这两类不同底物的结合并不相同。
