The problem of negative results for styrene in the in vitro mutagenesis test with metabolic activation (microsomal assay). - 2. Behaviour of epoxide hydrolase in the incubation mixtures.

The behaviour of epoxide hydrolase and monooxygenase was studied in incubation mixtures for the in vitro mutagenesis test with metabolic activation (microsomal assay) both in the presence and in absence of styrene 50mM. Epoxide hydrolase activity was much more stable than monooxygenase in all tested systems (S-9 fractions or microsomes of rats or mice, males or females) both in the presence and in absence of styrene. Membrane bound epoxide hydrolase was slightly less stable than the soluble one. These results further substantiate the explanation for the negative results of in vitro mutagenesis tests with styrene.