EPN [O-Ethyl O-p-nitrophenyl phenylphosphonothioic acid] 
Liver homogenates from several species of mammals, birds and fish 
were used to study nitroreductase activity. A comparison of the data 
showed that enzymatic activity varied between classes and among species 
within a given class of animals. Although reduction of the nitro group 
to the amino group probably proceeded via the nitroso and hydroxylamino 
derivatives, the presence of neither one was detected. Species tested 
included: rat, mouse, guinea pig, chicken, English sparrows, bullhead, 
sucker, flounder, sculpin, large mouth bass, sunfish, bluegill, alewife. 
Distribution of nitroreductase in rats varied among tissues: liver > 
kidney > spleen > heart > lung > erythrocytes > plasma =0. In English 
Sparrows and chickens, activity in kidney exceeded that in liver (669). 
Rabbit sera brought about removal of sulfur and hydrolysis to p-nitro- 
phenol (1078). 
Under culture conditions, B. subtilis reduced EPN to amino EPN 
(1018). 
Ultraviolet irradiation of various formulations of EPN showed de- 
creasing stability in the order: Dust > emulsifiable concentrate> wet- 
table power > pure EPN. Stability also decreased as the concentrations 
of EPN decreased. The half-lives for 1073, box 10-4, and 3 x 1074 di- 
lutions of 50% emulsifiable concentrate were 3.7, 2.1, and 1.3 hours, 
respectively (1104). 
When EPN was irradiated for 10 hours by ultraviolet, in addition 
to a resin and unchanged EPN, p-nitrophenol and thiophosphonate were 
identified by color reactions and infrared spectra. Another compound, 
which did not possess a P + S linkage, was presumed to be O-ethyl O- 
(p-nitrophenyl) benzenephosphonate from infrared spectra (1106). 
Rabbit sera converted EPN, to p-nitrophenol (1078). After incu- 
bation of EPN with NADPH», oxygen and microsomes of rat, housefly, or 
rabbit liver, the corresponding phenol was found in each case. The oxon 
analog was also produced. Some conversion of the oxon to the corresponding 
phenol was also observed (1700). 
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