title: Substrate specificity of carboxylesterase isozymes and their contribution to hydrolase activity in human liver and small intestine.
abstract: Hydrolase activity from human liver and small intestine microsomes was compared with that of recombinant human carboxylesterases, hCE-1 and hCE-2. Although both hCE-1 and hCE-2 are present in human liver, the dominant component was found to be hCE-1, whereas the hydrolase activity of the human small intestine was found to be predominantly hCE-2. hCE-2 has a limited ability to hydrolyze large acyl compound substrates. Interestingly, propranolol derivatives, good substrates for hCE-2, were easily hydrolyzed by substitution of the methyl group on the 2-position of the acyl moiety, but were barely hydrolyzed when the methyl group was substituted on the 3-position. These findings suggest that hCE-2 does not easily form acylated intermediates because of conformational interference in its active site. In contrast, hCE-1 could hydrolyze a variety of substrates. The hydrolytic activity of hCE-2 increased with increasing alcohol chain length in benzoic acid derivative substrates, whereas hCE-1 preferentially catalyzed the hydrolysis of substrates with short alcohol chains. Kinetic data showed that the determining factor for the rate of hydrolysis of p-aminobenzoic acid esters was V(max) for hCE-1 and K(m) for hCE-2. Furthermore, the addition of hydrophobic alcohols to the reaction mixture with p-aminobenzoic acid propyl ester induced high and low levels of transesterification by hCE-1 and hCE-2, respectively. When considering the substrate specificities of hCE-1, it is necessary to consider the transesterification ability of hCE-1, in addition to the binding structure of the substrate in the active site of the enzyme.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-Honmachi, Kumamoto 862-0973, Japan. iteruko@gpo.kumamoto-u.ac.jp
authors.forename: Teruko
authors.initials: T
authors.lastname: Imai
authors.forename: Megumi
authors.initials: M
authors.lastname: Taketani
authors.forename: Mayumi
authors.initials: M
authors.lastname: Shii
authors.forename: Masakiyo
authors.initials: M
authors.lastname: Hosokawa
authors.forename: Kan
authors.initials: K
authors.lastname: Chiba
mesh_terms: D000818:Animals; D001565:Benzoates / Q000737:chemistry / Q000378:metabolism; D043182:Carboxylesterase / Q000235:genetics / Q000378:metabolism*; D002265:Carboxylic Ester Hydrolases / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D005480:Flurbiprofen / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006867:Hydrolases / Q000378:metabolism*; D006868:Hydrolysis; D007421:Intestine, Small / Q000201:enzymology* / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008099:Liver / Q000201:enzymology* / Q000378:metabolism; D008861:Microsomes / Q000201:enzymology / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D015394:Molecular Structure; D011433:Propranolol / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D001565:Benzoates; D007527:Isoenzymes; D005480:Flurbiprofen; D011433:Propranolol; D006867:Hydrolases; D002265:Carboxylic Ester Hydrolases; C474609:CES1 protein, human; C517204:CES2 protein, human; D043182:Carboxylesterase