Enzymatic hydrolysis of structurally diverse phthalic acid esters by porcine and bovine pancreatic cholesterol esterases

A weak hydrolyzing activity against bis (2-ethylhexyl) phthalate (DEHP) was discovered in a commercial crude lipase (EC 3.1.1.3) preparation from porcine pancreas. DEHP was hydrolyzed to mono (2-ethylhexyl) phthalate (MEHP) not by a pancreatic lipase but by a cholesterol esterase (CEase, EC 3.1.1.13), a trace contaminant in the crude lipase preparation. Enzymatic hydrolysis of phthalic acid esters (PAEs), suspected to be endocrine-disrupting chemicals, was investigated using CEases from two species of mammals and a microorganism. Eight structurally diverse PAEs, namely diethyl phthalate (DEP), di-n-propyl phthalate (DPrP), di-n-butyl phthalate (DBP), di-n-pentyl phthalate (DPeP), di-n-hexyl phthalate (DHP), DEHP, n-butyl benzyl phthalate (BBP), and dicyclohexyl phthalate (DCHP), were hydrolyzed to their corresponding monoesters by both porcine and bovine pancreatic CEases, while a microbial CEase from Pseudomonas sp. had no hydrolyzing activity against these PAEs. The hydrolysis experiments with bovine pancreatic CEase (50 U) indicated complete hydrolysis of every PAE (5 μmole) except for BBP and DCHP within 15 min; BBP and DCHP were hydrolyzed within 30 min and 6 h, respectively. The rates of PAE hydrolysis could be affected by the bulkiness of alkyl side chains in the PAEs. This study provides important evidence that mammalian pancreatic CEases, such as those from porcine and bovine sources, are potential enzymes for nonspecific degradation of structurally diverse PAEs.