Enantioselectivity of microsomal and cytosolic esterases in rat intestinal mucosa.
Enantioselectivity of esterases, contained in 9,000g supernatant fraction (S9) prepared from homogenate of small intestinal mucosa of male Sprague-Dawley rats and the subsequent 105,000g supernatant (cytosol) and pellet (microsomes) prepared from S9, was studied using racemic oxazepam 3-acetate (rac-OXA) as the substrate. Esterases in S9 were enantioselective in hydrolyzing either S-OXA or R-OXA, depending on a particular subcellular preparation. Cytosolic and microsomal esterases had opposite enantioselectivity and selectively hydrolyzed S-OXA and R-OXA, respectively. Enantioselectivity of esterases solubilized from microsomes with Triton X-100 (0.1%, w/v) was identical to that of the membrane-bound microsomal esterases. Cytosolic esterases were more sensitive to temperature than either solubilized or membrane-bound microsomal esterases. In the presence of paraoxon (1 microM), the esterases selective toward R-OXA in both microsomes and S9 were completely inhibited, whereas the esterases selective toward S-OXA in cytosol were inhibited by approximately 6%. These results indicate that cytosolic and microsomal esterases in rat small intestinal mucosa are distinctly different enzymes, with opposite enantioselectivity in the hydrolysis of rac-OXA.
Yang
S K
SK
Department of Pharmacology, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences.
Hsieh
Y Y
YY
Chang
W C
WC
Huang
J D
JD
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000201:enzymology*; D004795:Enzyme Stability; D004950:Esterases / Q000032:analysis* / Q000037:antagonists & inhibitors / Q000302:isolation & purification; D007413:Intestinal Mucosa / Q000201:enzymology*; D008297:Male; D008861:Microsomes / Q000201:enzymology*; D010076:Oxazepam / Q000378:metabolism; D010261:Paraoxon / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013237:Stereoisomerism
D010076:Oxazepam; D004950:Esterases; D010261:Paraoxon