A method for the extensive purification of rabbit liver cytoplasmic epoxide hydrolase is described. The endproduct, which was purified 550-fold with respect to the cytosolic fraction, appeared to be more than 85 ' %, pure. Results indicate that the enzyme is a dimer of molecular weight I10000 and consists of two subunits,which are identical or very similar ( M , 57000) and possess N-terminal serine. Evidence for the existence of aggregates of higher molecular weight was also obtained. The catalytic properties of the cytoplasmic enzyme with styrene oxide as substrate ( K , = 3.4 m M ; V = 3480 nmol mg-' min-') differed markedly from the values published for the microsomal hydrolase.
Using trans‐stilbene oxide as substrate, the subcellular distribution of epoxide hydrolase was investigated in livers from DBA/2 mice. The highest specific activities were found in cytosolic and light mitochondrial fractions. Isopycnic subfractionation of the light mitochondrial fraction showed that the organelle‐bound trans‐stilbene oxide hydrolase is localized in peroxisomes.
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