The covalent binding of 3-methylindole metabolites to bovine tissue

Tritiated 3-methylindole (3MI) was administered intravenously to calves. Total and covalent bound radioactivity were measured in different tissues. Pulmonary tissue showed the highest concentration of covalent bound radioactivity. (G-³H) or (methyl-¹⁴C) 3MI became covalently bound to microsomal protein when incubated with bovine lung microsomes. This covalent binding was dependent on time, temperature, oxygen and NADPH and was inhibited by SKF-525A, cytochrome c, a carbon monoxide enriched atmosphere and cysteine. The microsomal enzyme system catalysing covalent binding of 3MI has the classical characteristics of a cytochrome P-450 dependent mixed function oxidase. Metabolic activation of 3MI to a highly electrophilic intermediate, may be fundamental in the pathogenesis of 3MI induced pulmonary damage.