Comparative studies of sheep lung and liver nitrofurantoin reductase

1. Nitrofurantoin reductase which catalyzes the bioactivation of nitrofurantoin was purified to electrophoretic homogenity from sheep liver and lung microsomes, with a yield of 15% and 35%, respectively. The specific activity of both reductases was found to be similar (140 nmol/min/mg protein). 2. The effects of nitrofurantoin and NADPH concentrations, pH, ionic strength, amount of enzyme and reaction period, on the enzyme activity were studied and the optimum conditions for maximum activity of purified liver and lung nitrofurantoin reductases were determined. 3. The enzyme concentration was found proportional with the square root of the rate of nitrofuratoin reduction up to approximately 15 micrograms protein/ml and 25 micrograms protein/ml incubation mixture for liver and lung nitrofurantoin reductases, respectively. 4. The plots of inverse of the nitrofurantoin concentration against the inverse of the square root of the velocity for the reduction of nitrofurantoin by liver and lung enzymes gave Km values as 27.78 microM and 32.25 microM, respectively. 5. The purified liver and lung enzymes were also saturated by NADPH at similar concentrations and the Km values were calculated as 29.4 microM and 35.5 microM, 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 the other ions inhibited the activity of both liver and lung reductases.