Lipid epoxide hydrolase in rat lung preparations

Area of Science:

• Biochemistry
• Enzymology
• Pharmacology

Background:

• Epoxide hydrolase (EC 3.3.2.3) plays a role in xenobiotic and endogenous epoxide metabolism.
• Lipid epoxides, including cholesterol epoxide, are found in lung tissue.
• Understanding epoxide hydrolase activity is crucial for metabolic studies.

Purpose of the Study:

• To investigate the activity of rat lung epoxide hydrolase using specific lipid epoxides.
• To compare the kinetic properties of lung epoxide hydrolase with liver epoxide hydrolase.
• To elucidate the interaction of cholesterol epoxide with lung epoxide hydrolase.

Main Methods:

• Enzyme kinetic assays using methyl cis-9,10-epoxystearate and cholest-5 alpha,6 alpha-epoxy-3 beta-ol.
• Isolation and characterization of microsomal and soluble epoxide hydrolase fractions from rat lung and liver.
• Competitive inhibition studies to determine substrate binding affinities.

Main Results:

• Rat lung epoxide hydrolase exhibited differential activity towards the tested epoxides, with methyl cis-9,10-epoxystearate being hydrated significantly faster than cholesterol epoxide.
• A soluble epoxide hydrolase was detected in both lung and liver, showing similar activity profiles to the microsomal enzyme.
• Liver epoxide hydrolase demonstrated higher activity than lung epoxide hydrolase for both substrates.
• Cholesterol epoxide acted as a potent competitive inhibitor of methyl cis-9,10-epoxystearate metabolism by lung microsomal epoxide hydrolase, despite its slow hydration rate.

Conclusions:

• Lung epoxide hydrolase displays substrate-dependent kinetics and varying Km values.
• Cholesterol epoxide exhibits high-affinity, nonproductive binding to lung microsomal epoxide hydrolase.
• The nonproductive binding of cholesterol epoxide may explain its high concentration in lung tissue.