active form. Recent theoretical and experimental studies point toward radical C-H activation as the initial reaction and rate limiting step. A possible alternative hydride transfer seems to be less likely. The mechanism concludes with conversion of the hydrocarbon to a carbocation intermediate and rebound of a hydroxide to form the hydroxylated product. Moreover, a histidine residue (His192) of the active site seems to be involved in the reaction mechanism. References EC 1.17.99 Enzymes of known structure