Klaus Krisch

The carboxylesterases/amidases of mammalian liver and their possible significance.

AbstractWith regard to the acyl moiety, carboxylesterases preferentially split esters of short-chain carboxylic esters. With most carboxylesterases the maximum of the reaction rate is found at an acyl chain length of C3 to C624,77,170,303 (see Section 5.4). However, there are some reports of carboxylesterases acting on medium- and long-chain fatty acid esters as well.143,189,252,253

Human liver carboxylesterase: Purification and molecular properties☆

An unspecific carboxylesterase was purified 180-fold from acid-precipitated human liver microsomes. The final preparation was homogeneous on disc electrophoresis and polyacrylamide gel electrophoresis in the presence of 6.25 M urea at pH 3.2. A single symmetrical peak was also found on gel filtration and on velocity sedimentation in the analytical ultracentrifuge, whereas slight heterogeneity was observed on isoelectric focusing. The amino acid composition of the purified enzyme is presented. From the results the partial specific volume (0.745 ml × g−1) and the minimal molecular weight (60,000) could be calculated. Fingerprint maps of tryptic peptides from the carboxymethylated enzyme are shown. The molecular weight as determined by gel filtration, disc electrophoresis, and analytical ultracentrifugation is in the range of 181,000–186,000. For the molecular weight of the subunits a value of 61,500 has been obtained by sodium dodecylsulfate polyacrylamide gel electrophoresis. The equivalent weight of the enzyme has been estimated to be 62,500 from stoichiometry of its reaction with diethyl-p-nitrophenyl-phosphate. Partial cross-linking of the subunits with dimethyl suberimidate and subsequent sodium dodecylsulfate polyacrylamide gel electrophoresis yielded three bands with molecular weights of 60,000, 120,000, and 180,000. From these results it is concluded that human liver esterase is a trimeric protein. It is composed of three subunits of equal size, and there is one active site per subunit.

Hydrolysis of steroid hormone esters by an unspecific carboxylesterase from pig liver microsomes

Abstract Twenty-two steroid esters, most of them therapeutically used as long-acting hormone preparations, were studied as in vitro substrates of an unspecific carboxylesterase from pig liver. All but four were hydrolysed. The activities were measured titrimetrically using the pH stat technique, and the kinetic parameters K m and K cat were determined. All Michaelis constants were found to be in the range of 10 −5 –10 −6 M. The enzymatic hydrolysis of most substrates followed Michaelis-Menten kinetics. Some deviations are discussed. Some experiments on the influence of acetonitrile, used as a solvent for all substrates, are reported.

Electron microscopy of pig liver carboxylesterase

During the past decade high-resolution electron microscopy has become increasingly important as an additional tool for elucidating the subunit structure of many enzymes [l] . In the present paper we wish to report an electron microscopic study of pig liver carboxylesterase (EC 3.1.1.1). This enzyme is a dissociating protein with a molecular weight of 163 000-168 000 as was found independently in three laboratories [2-41 ; its subunit composition, however, is still controversial [5,6].