The effect of Hg 2+ on rabbit hepatic and pulmonary solubilized, partially purified N,N-dimethylaniline N-oxidases

Abstract

Solubilization and partial purification of the rabbit pulmonary and hepatic N,N-dimethylaniline N-oxidases were carried out in order to study the effect of Hg 2+ in vitro observed previously in the microsomal enzymes. Rabbit lung microsomal N,N-dimethylaniline (DMA) N-oxidase activity was stimulated 1.5–2 times by 0.1 mM Hg 2+ added in vitro. This concentration of mercury inhibited hepatic microsomal N-oxidase by 50%. Upon solubilization and partial purification of the lung N-oxidase enzyme, stimulation of the N-oxidase activity by 0.1 mM Hg 2+ was lost. It was found that the concentration of Hg 2+ that would stimulate the partially purified pulmonary N-oxidases was 25 μM or less. Stimulation by 0.1 mM Hg 2+ of the partially purified N-oxidase from lung was restored by addition of flavins (FMN or FAD) or a heat-stable (NH 4) 2SO 4 precipitated fraction obtained during the purification of the N-oxidase from solubilized pulmonary or hepatic microsomes. However, addition of the flavins or the solubilized, heat-stable fraction from liver or lung microsomes did not reverse inhibition by 0.1 mM Hg 2+ of the N-oxidase in hepatic microsomes or in partially purified preparations from these hepatic microsomes. Kinetic data suggest that flavins and the heatstable factor isolated from microsomes lower the concentration of free Hg 2+. The determination of kinetics of Hg 2+ inhibition (liver) and activation (lung) with the partially purified N-oxidases showed that the pulmonary and hepatic DMA N-oxidase enzymes are markedly different with respect to their in vitro response to Hg 2+. This suggests that the N-oxidases from liver and lung may be different enzymes.