Cholesterol Ester Hydrolase Mediated Conjugation of Haloethanols with Fatty Acids

The formation of fatty acid conjugates of haloethanols was studied under in vitro conditions by using purified bovine pancreatic cholesterol ester hydrolase (EC 3.1.1.13). The enzymatic formation of 2-chloroethyl and 2-bromoethyl esters of oleic, linoleic, linolenic, and arachidonic acids was confirmed by proton nuclear magnetic resonance spectroscopy and chemical ionization mass spectrometry. 2-Bromoethanol was a better substrate than 2-chloroethanol for fatty acid esterification using cholesterol ester hydrolase. Among the chloroethanols, 2-chloroethanol was a better substrate than 2,2-dichloroethanol and 2,2,2-trichloroethanol. The saturated fatty acids (palmitic and stearic) showed a small amount of ester formation when cholesterol ester hydrolase was used. The kinetics of haloethanol and oleic acid incorporation into haloethyl oleate catalyzed by cholesterol ester hydrolase were determined. In vitro experiments were also conducted to study the conjugation of haloethanols with fatty acids using rat liver microsomes. The saturated fatty acid (palmitic) was more reactive compared to unsaturated fatty acid (oleic) when haloethanols were used. The results using rat liver microsomes were in contrast to those obtained when cholesterol ester hydrolase was used. The synthesis, purification, and characterization of 2-chloroethyl and 2-bromoethyl esters of oleic, linoleic, linolenic, and arachidonic acids are also described.