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The low reactivity of 5H-dibenzo[a, d]cycloheptene 10,11-oxide in microsomal epoxide hydrolase catalysed hydration.

1. The rate of hydration of 5H-dibenzo[a, d]cycloheptene 10,11-oxide catalysed by rabbit liver microsomal epoxide hydrolase has been compared with that of the acyclic analogue cis-stilbene oxide. The latter was shown to be a much better substrate for the enzyme than the former epoxide. 2. The kinetic parameters for the hydration of 5H-dibenzo[a,d]cycloheptene 10,11-oxide and cis-stilbene oxide have been determined using a rabbit liver microsomal preparation at 37 degrees C and pH 7.4. The much slower hydration of the former is due to a much lower Vs and not to a higher Km relative to the latter epoxide. 3. 5H-Dibenzo[a,d]cycloheptene 10,11-oxide inhibited the hydration of cis-stilbene oxide by rabbit liver microsomal epoxide hydrolase.