title: Organophosphate inhibitors: the reactions of bis(p-nitrophenyl) methyl phosphate with liver carboxylesterases and alpha-chymotrypsin.
abstract: Bis(p-nitrophenyl) methyl phosphate (BNMP) has been tested as a spectrophotometric titrant for a group of serine hydrolases. Bis(p-nitrophenyl) methyl phosphate reacts rapidly with liver carboxylesterases from chicken, sheep, and horse, and more slowly with alpha-chymotrypsin, releasing 2 mol of p-nitrophenol per active site titrated, and producing a phosphorylated enzyme very stable to dephosphorylation. However, pig liver carboxylesterase produces 2.2 mol of p-nitrophenol per active site titratedmreaction of pig and chicken liver carboxylesterases with bis(p-nitrophenyl) [3H]methyl [32P]phosphate clarified this differencemone molecule of the chicken enzyme reacts with one molecule of bis(p-nitrophenyl) methyl phosphate, releasing both p-nitrophenol residues, and resulting in an inhibited enzyme with one phosphorus atom and one methyl group covalently bound. Pig enzyme reacts rapidly, forming (presumably) methyl p-nitrophenyl phosphoryl-carboxylesterasemthis further reacts, concurrently producing methyl phosphoryl-carboxylesterase plus p-nitrophenol, or free enzyme plus methyl p-nitrophenyl phosphate, in the ratio of about 5 : 1 at pH 7.55. The free enzyme produced undergoes further reaction with bis(p-nitrophenyl) methyl phosphate until all the carboxylesterase is inhibited.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002645:Chickens; D002918:Chymotrypsin; D004950:Esterases; D006736:Horses; D007531:Isoflurophate; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008970:Molecular Weight; D009596:Nitrophenols; D009943:Organophosphorus Compounds; D011485:Protein Binding; D012756:Sheep; D013045:Species Specificity; D013552:Swine
chemical_list: D009596:Nitrophenols; D009943:Organophosphorus Compounds; D007531:Isoflurophate; D004950:Esterases; D002918:Chymotrypsin