Phosphorsäur e-bis-[p-nitro-phenylester], ein neuer Hemmstoff mikrosomaler Carboxylesterasen

Abstract

Bis-[p-nitro-phenyl]phosphate reacts rapidly, irreversibly and stoichiometrically with a highly purified preparation of carboxylesterase (EC 3.1.1.1) from pig liver microsomes. The product is a phosphorylated, inactive enzyme derivative. With an excess of the inhibitor, two moles of p-nitro-phenol are released for each mole of enzyme. This confirms earlier studies with E 600 [diethyl-p-nitrophenyl phosphate] which indicated that pig liver esterase has 2 active centers. Two other carboxylesterases from bovine liver and from pig kidney are also inhibited by bis-[p-nitro-phenyl]phosphate. [alpha]-Chymotrypsin, trypsin, acetylcholinesterase and non-specific serum cholinesterase are, however, not inhibited. The LD50 for bis-[p-nitro-phenyl]phosphate (intraperitoneal) in the mouse is 410 mg/kg. The hydrolysis of monoethylglycine-2,6-xylidide by mouse liver is also blocked in vivo by this phosphate ester. Kinetic studies show that the 2nd active center of carboxylesterase from pig liver reacts about 10 times more slowly than the 1st with bis-[p-nitro-phenyl]phosphate. The activation enthalpy and pH-optima were measured for the reaction with the 1st active center.