Fatty acid conjugation of
alcohols, catalyzed by
fatty acid ethyl ester synthase (FAEES), results in the formation of lipophilic
esters. Although the activity of FAEES is reported in almost all organs, including plasma, the interrelationship among various
proteins expressing FAEES activity in different organs/tissues is not well understood. Earlier, we have reported an inhibition of FAEES activity in human
hepatoma cells by tri-o-tolylphosphate (
TOTP;
serine esterase inhibitor). The present study was undertaken to further characterize the hepatic, plasma, and pancreatic FAEES in rats after ip injection of 10, 25, 50, or 100 mg/kg
TOTP in
corn oil or vehicle alone. After 18 h, animals were euthanized and FAEES activity in the plasma and postnuclear fractions of hepatic and pancreatic homogenates were assayed by measuring the
ester formation following incubation with [1-(14)C]
oleic acid and
ethanol or
methanol as substrates. Significant inhibition of FAEES activity was observed in hepatic postnuclear fraction. The
esterase activity also showed a pattern similar to
fatty acid ethyl and methyl
ester synthesizing activity. A trend similar to hepatic synthesizing and hydrolyzing activities was also found in the plasma of
TOTP-treated rats. However, no inhibition of synthetic activity toward formation of
fatty acid ethyl or methyl
esters or
p-nitrophenyl acetate hydrolyzing activity was observed in the pancreas of rats after
TOTP exposure. Our results also show that the
protein expressing FAEES activity in the pancreas does not cross-react with
antibodies to rat adipose tissue FAEES using Western blot analysis, which recognizes approximately 60- and approximately 84-kDa
proteins in the liver and plasma, respectively. Furthermore, the inhibition in liver is at the functional level of
enzyme as no change was observed between control and treated animals by immunohistochemistry. We conclude that
fatty acid ethyl or methyl
ester synthesizing
enzyme(s) in the liver and plasma, which are inhibited by
TOTP, are different from that present in the pancreas.