COMPARATIVE-STUDIES OF SHEEP LUNG AND LIVER NITROFURANTOIN REDUCTASE

1. Nitrofurantoin reductase which catalyzes the bioactivation of nitro furantoin was purified to electrophoretic homogenity from sheep liver and lung microsomes, with a yield of 15% and 35%, respectively. The sp ecific activity of both reductases was found to be similar (140 nmol/m in/mg protein). 2. The effects of nitrofurantoin and NADPH concentrati ons, pH, ionic strength, amount of enzyme and reaction period, on the enzyme activity were studied and the optimum conditions for maximum ac tivity of purified fiver and lung nitrofurantoin reductases were deter mined. 3. The enzyme concentration was found proportional with the squ are root of the rate of nitrofurantoin reduction up to approximately 1 5 mug protein/ml and 25 mug protein/ml incubation mixture for liver an d lung nitrofurantoin reductases, respectively. 4. The plots of invers e of the nitrofurantoin concentration against the inverse of the squar e root of the velocity for the reduction of nitrofurantoin by liver an d lung enzymes gave K(m) values as 27.78 muM and 32.25 muM, respective ly. 5. The purified liver and lung enzymes were also saturated by NADP H at similar concentrations and the K(m) values were calculated as 29. 4 muM and 35.5 muM, respectively. 6. The effects of magnesium, nickel, cadmium and copper ions on the nitrofurantoin reductase activity were examined. Magnesium ion was found to have almost no effect, whereas t he other ions inhibited the activity of both liver and lung reductases .