Oxidation of Dimethylselenide to Dimethylselenoxide by Microsomes from Rat Liver and Lung and by Flavin-Containing Monooxygenase from Pig Liver

Oxidation of [75Se]dimethylselenide by rat liver and lung microsomes and by purified flavin-containing monooxygenase from pig liver was demonstrated. Quantitation of the nonvolatile product showed a 1:1 stoichiometry with NADPH oxidation, consistent with selenoxide formation. The apparent Km for dimethylselenide was 0.7 μM with rat liver microsomes and 0.3 μM with purified pig liver enzyme. Facile reversal of dimethylselenide oxidation by reducing agents present in microsomes, and by glutathione, indicates that redox cycling can occur. Unlabeled dimethylselenoxide carrier circumvented reduction of the labeled product, permitting quantitation. This is the first demonstration of a naturally occurring selenium substrate for the microsomal flavin-containing monooxygenase.