Purification and Properties of Two Carboxylesterases from Rat‐Liver Microsomes

Abstract

The esterase activity of rat liver was mainly concentrated in the microsomal and nuclear fractions, with low activities in other fractions. On the basis of sensitivity t o certain esterase inhibitors, the microsomal esterases were considered to be of a carboxylesterase type. The esterase distribution in sonicated rough microsomes, separated by zone centrifugation, was also investigated.Solubilization of the microsomal esterases was achieved by sodium deoxycholate, trypsin and phospholipase-A treatment. Two esterases were solubilized from rat-liver microsomes by phospholipase-A treatment and were further purified by Chromatography on Sephadex G-100 and DEAE-cellulose. The enzymes were purified 256 and 154 times. The isoelectric points, K , values and molecular weights of the two esterases were determined.Both enzymes are of a carboxylesterase type. One of the esterase, however, was sensitive to HgCl, of low concentrations, which is an unusual property for carboxylesterases. The question of whether the two enzymes constitute a monomer and a dimer of the same esterase or are completely different enzymes, is discussed, The cellular distribution of esterases in the livers of different species has been reported frequently. The microsomal fraction seems to be the main source of the carboxylesterases [l -41, where, as this paper will show, they are bound to the microsomal membrane.

Catalytic Properties of an Unspecific Carboxylesterase (E1) from Rat‐Liver Microsomes

“…This is in good agreement with the pH optima reported for other carboxylesterases [Z, 12,171. The corresponding profile for methyl butyrate, however, was dependent on the substrate concentration (Fig.5).…”

Characterization of pyrethroid hydrolysis by the human liver carboxylesterases hCE-1 and hCE-2

“…Three replicates were conducted for each compound with the same enzyme preparations. Hydrolytic activity for pNPA was monitored for 2 min at 405 nm in 96-well, flat-bottomed, polystyrene microtiter plates (Dynex Technologies, Chantilly, VA) and analyzed on a Spectramax 200 plate reader (Molecular Devices, Sunnyvale, CA) according to the methods of Ljungquist and Augustinsson [14] as modified in Wheelock et al [15].…”

Substrate specificity of purified rabbit liver esterase ES‐1

“…Comparison of substrate specificity observed in the present study for rabbit liver ES-IA with that reported in the literature for rat liver ES-10. In the literature, rat liver carboxylesterase ES-10 was referred to as follows: hydrolase PI 6.0 [5,14,28,[36][37][38]461; PI 6.1 csterase [42,43]; esterase El [4,39,41,44]; carboxylesterase RHI [34, 401; esterase el [35]; esterase I1 [45] [4,5,28,[34][35][36][37][38][39][40] [401 [4, 28, 39, 401 15, 351 [4> 281 14, 281 44, 45, 471 [4,281 [4> 281 [4,281 [4> 281 [5,451 1451 14, 14, 281 [4, 51 [41-431 [4, 5, 28, 36-38, 41 ~5,421 [34,401 ~14,401 ~5,141 [51 ~5,141 [4,5, 141 1461 1461 141 ~5,141 [4, 5, 14, 28, 36-41] logical substrates were poorly hydrolysed (Table 3). The octanoylglycerol esters were hydrolysed, but compounds such as acetylcholine, butyrylcholine and butyrylthiocholine were not hydrolysed.…”