36] Cytosolic liver Enzymes catalyzing hydrolysis of leukotriene A4 to leukotriene B4 and 5,6-dihydroxyeicosatetraenoic acid

Abstract

Publisher Summary The chapter focuses on LTA 4 hydrolase and cytosolic epoxide hydrolase from guinea pig and mouse liver, respectively. The methods have a broader application because extended studies with synthetic LTA 4 and xenobiotic epoxides have shown that both enzymatic activities have a widespread occurrence in mammalian tissues. Enzymatic hydrolysis of LTA 4 may be catalyzed by two different enzymes with several functional and structural differences). Thus, LTA 4 hydrolase (EC 3.3.2.6) converts the epoxide into LTB 4 , whereas cytosolic epoxide hydrolase (EC 3.3.2.3) generates 5( S ),6( R )-dihydroxy-7,9- trans -11,14- cis -eicosate-traenoic acid (5,6-DiHETE). Epoxide hydrolases, microsomal or cytosolic, are believed to be involved in detoxification of various harmful xenobiotic epoxides. Cytosolic (and microsomal) epoxide hydrolase has a broad substrate specificity and has frequently been characterized with stable aromatic and aliphatic xenobiotic epoxides. Performing enzyme kinetic experiments with LTA4 confronts the investigator with the problem of substrate instability. The chapter discusses general procedures for incubations and extractions, characterization of enzymatic hydrolysis products, subcellular distribution of epoxide hydrolase and LTA 4 hydrolase in liver tissue, purification of LTA4 hydrolase from guinea pig liver cytosol, and several related products.