Abstract
1. The nitro-reducing capacity of the mammalia in vitro was discussed.
2. The liver, kidneys, heart, muscle, lung, testicles, spleen, uterus, vagina, and ovary of rats were homogenized and examined, and the former seven were found able to reduce p-nitrophenol in the above order.
3. The reduction of the nitro group by the liver is inhibited by cyanide, monoiodoacetic acid, sodium azide, and thiourea, suggesting the indispensable participation of heavy metals in the reduction mechanism.
4. Dialysis removed the reducing capacity of the liver, which is restored by the addition of a boiled juice of the liver, succinate, glucose plus DPN, and alcohol plus DPN.
5. Acetone precipitation also removed the capacity, which was restored by the addition of the boiled juice, glucose and alcohol with DPN.
6. The acetone fractionation of the liver homogenate affords a fraction which possesses nitro-reducing capacity only when coupled with alcohol dehydrogenase system (alcohol plus alcohol dehydrogenase plus DPN). The alcohol dehydrogenase system failed to reduce p-nitrophenol in the absence of the nitroreductase fraction of the liver.
7. The difference in the order of the distribution between the nitro-reducing capacity and succinic dehydrogenase activity was shown and the existence of an enzyme was discussed which plays an indispensable role directly in the reduction of the aromatic nitro group in the mammalia. This enzyme may be termed a “mammalian nitroreductase.”
