Specificity of human, rat and mouse skin epoxide hydratase towards K-region epoxides of polycyclic hydrocarbons

Epoxide hydratase activity has been measured in microsomal fractions of skin from mouse, rat and humans. The skin enzyme was able to hydrate all epoxides tested. The specific enzyme activities decreased in the order human > mouse > rat. The relative activity towards K-region epoxides of various polycyclic hydrocarbons in skin microsomal fractions from all three species decreased in the order phenanthrene 9,10-oxide > benz(a)anthracene 5,6-oxide ? benzo(a)pyrene 4,5-oxide ? 7-methylbenz(a)anthracene 5,6-oxide > 3-methylcholanthrene 11,12-oxide > dibenz(a,h)anthracene 5,6-oxide. The activity of epoxide hydratase in human skin microsomal fractions showed little pH dependence and was inhibited by small molecular weight inhibitors in a manner similar to that of the liver microsomal enzyme. Interindividual variation of epoxide hydratase activity in skin microsomal fractions from six human subjects was considerable, namely from 175 to 447 pmoles benzo(a)pyrene 4,5-dihydrodiol/min per mg protein. This variation was not due to skin disease or treatment and had no apparent correlation with age or sex. A possible correlation with the part of the body from which the skin sample was taken could not be excluded since the activity in skin samples from the abdomen seemed lower than that in samples from leg or breast.