Plant biochemistry of xenobiotics. Purification and properties of a wheat esterase hydrolyzing the plasticizer chemical, bis(2-ethylhexyl)phthalate

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Abstract
A soluble wheat esterase, catalyzing a cleavage of the mass-produced plasticizer chemical, bis(2-ethylhexyl)phthalate (DEHP), was discovered. Although wheat plants and seeds as well as cultured wheat cells contained > 12 nonspecific esterase activities, only a single protein with a marked preference for a substrate chain-length of 6-8 C atoms was active with DEHP. This enzyme differed from all previously characterized plant lipases and esterases. The enzyme was purified 10-fold from wheat plants and 280-fold, to electrophoretic homogeneity, from cultured wheat cells. An apparent functional molecular mass of 38,000 Da [dalton] and an apparent subunit molecular mass of 22,000 Da were determined. Inhibitor experiments pointed to the catalytic involvement of a serine residue. Cleavage of DEHP by the purified enzyme was .apprx. 104 times slower than cleavage of 4-nitrophenyl octanoate. This was consistent with previous evidence for a rate-limiting role of the esterase reaction in DEHP metabolism by intact wheat cells.

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