Studies on nitrazepam reduction in vitro

The solvents decreased the reduction rate of nitrazepam by rat liver homogenate; the lowest interference was observed with ethanol. High concentrations of nicotinamide used in media for nitroreductase determination lowered enzyme activity. Reduction of nitrazepam to 7-amino derivative decreased during the preservation of liver centrifugal fractions in 1.15% KCl at 0°C. The highest enzyme activity was found in rat liver, followed by the activity of kidney, heart, lung, skeletal muscle and spleen preparations. The substance was not reduced in brain. The Michaelis constants K_m of nitrazepam reduction did not differ substantially, being of the same order of 10^-4M in preparations from rat, mouse, rabbit and guinea pig liver. The maximal velocities of the reduction V_max were 10^-6moles per hour per 1 g of liver tissue. Chlorpromazine, diazepam and imipramine influenced the reduction only in high concentrations. EDTA, cysteine and ascorbic acid did not change substantially the enzyme activity. KCN was a strong non-competitive inhibitor (K_i = 10^-4 M of the nitrazepam reduction.