The Oxidation of Foreign Compounds by Fly and Mouse Enzymes

Abstract

1. Aromatic ring hydroxylation of biphenyl, O-dealkylation of benzene, biphenyl, methylumbelliferone and fluorescein ethers, epoxidation of aldrin, alkyl oxidation of substituted toluenes, and the metabolism of carbamates and γ-PCCH, have been examined in preparations from mouse liver and housefly and blowfly abdomens. Enzymes from mice and flies, were localised in microsomes, required NADPH and oxygen, were inhibited by similar molecules, formed similar products and had similar substrate specificities. 2. Activities of fly enzymes were altered by systems liberated during the preparation procedures. Head and thorax contained a heat-stable, low molecular weight, RNA-bound inhibitor whose action was blocked by cyanide. Vigorous homogenisation of housefly abdomens liberated a heat-labile factor which reversibly inactivated oxidation enzymes. Its action was reversed by cyanide or rotenone or by some purified proteins including bovine serum albumin. A third system modified activities at high enzyme concentrations by limiting the time over which enzyme metabolised, substrate at a constant rate. The identities of these inhibitors are discussed and procedures minimising their effects described. 3. Oxidising activities towards biphenyl and aldrin developed at different rates in flies and the two activities were differentially inhibited by some structural analogues of the triphenylmethanes fluorescein and phenolphthalein. The hydroxylations of biphenyl and the O-dealkylations of biphenyl and methylumbelliferone ethers were inhibited together in enzymes from mice or flies. Although metabolic activities towards aldrin and γ-PCCH were inhibited by similar molecules and developed at similar rates in adult flies the metabolism of γ-PCCH did not involve an oxidative path in housefly enzymes. 4. Tissue concentration affected the rate of metabolism and the degree of inhibition of insect and vertebrate oxidation enzymes. These differences, which may have been caused by the distinctive interactions of microsomes with their substrates, indicate that results obtained in vitro may not quantitatively reflect oxidising ability and inhibition in living animals.