Cytochrome P-450 appears to catalyse most monooxygenation reactions by sequential one-electron steps rather than by a single, concerted transfer of the ferryl oxygen to the substrate. The radical intermediates, although very short-lived, can rearrange or undergo alternative reactions characteristic of radical species. As Paul Ortiz de Montellano explains, these alternative reactions yield novel metabolites, sometimes result in inactivation of the enzyme, and can provide information on the reaction mechanism.