COMPARISON OF ANILINE HYDROXYLATION BY HEMOGLOBIN AND MICROSOMAL CYTOCHROME-P450 USING STABLE ISOTOPES

Hemoglobin (Hb) and cytochrome P450 carry out aromatic ring hydroxylation of aniline. In the presence of reductants and Hb, para- and ortho-aminophenol were formed. Under [O-18]O-2, 100% of product was labeled; no incorporation occurred with [O-18]H2O. Deuterium (1.9%) was detectable in p-aminophenol formed from p-[H-2]aniline by Hb, as compared with 6% retention observed with cytochrome P450. These observations are consistent with a mechanism for Hb-dependent reaction involving formation of an iron-oxo complex competent to hydroxylate substrate. Hb-mediated reactions may represent a source of extra- hepatic metabolism since Hb is a major carrier for small organic molecules. The similarities of P450- and Hb-mediated aniline hydroxylation using stable isotopes preclude their use as in vivo probes.