Substrate specificity of carboxylesterase isozymes and their contribution to hydrolase activity in human liver and small intestine

Drug Metab Dispos. 2006 Oct;34(10):1734-41. doi: 10.1124/dmd.106.009381. Epub 2006 Jul 12.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Benzoates / chemistry
  • Benzoates / metabolism
  • Carboxylesterase / genetics
  • Carboxylesterase / metabolism*
  • Carboxylic Ester Hydrolases / genetics
  • Carboxylic Ester Hydrolases / metabolism*
  • Cell Line
  • Flurbiprofen / chemistry
  • Flurbiprofen / metabolism
  • Humans
  • Hydrolases / metabolism*
  • Hydrolysis
  • Intestine, Small / enzymology*
  • Intestine, Small / metabolism
  • Isoenzymes / genetics
  • Isoenzymes / metabolism
  • Liver / enzymology*
  • Liver / metabolism
  • Microsomes / enzymology
  • Microsomes / metabolism
  • Microsomes, Liver / enzymology
  • Microsomes, Liver / metabolism
  • Molecular Structure
  • Propranolol / chemistry
  • Propranolol / metabolism
  • Substrate Specificity


  • Benzoates
  • Isoenzymes
  • Flurbiprofen
  • Propranolol
  • Hydrolases
  • Carboxylic Ester Hydrolases
  • CES1 protein, human
  • CES2 protein, human
  • Carboxylesterase