Comparative studies of sheep liver and lung microsomal aniline 4-hydroxylase

1. The specific activity of the aniline 4-hydroxylase which catalyses hydroxylation of aniline to p-aminophenol was found to be 0.65 (N = 10) and 0.15 (N = 13) nmol p-aminophenol formed/mg protein/min, in sheep liver and lung microsomes, respectively. 2. The effects of aniline concentration, pH, cofactors, amount of enzyme and incubation period, on enzyme activity were studied, and the optimum conditions for maximum activity of liver and lung microsomes were determined. 3. Liver and lung microsomal aniline 4-hydroxylase activity was found to be completely dependent on the presence of cofactor NADPH. 4. The Lineweaver Burk and Eadie Hofstee plots of the liver enzyme were found to be curvilinear, suggesting that the enzyme did not follow the Michaelis Menten kinetics. From these graphs, two different Km values were calculated for the liver enzyme as 3.21 and 0.072 mM aniline. Km of the lung enzyme was calculated to be 1.43 mM aniline from its Lineweaver Burk graph. 5. The effects of magnesium, nickel and cadmium ions on the liver and lung aniline 4-hydroxylase activity were examined. Magnesium ion was found to have stimulatory effect, whereas nickel and cadmium ions inhibited the activity of the both liver and lung enzyme.