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1. After i.p. injection of [2,3-14C]acrylonitrile to rats, a significant portion of radioactivity becomes irreversibly attached to proteins of liver, lung, spleen and other tissues. 2. When rat liver microsomes were incubated with [2,3-14C]acrylonitrile, a time-dependent irreversible binding of radioactivity occurred to microsomal proteins. This binding was not dependent on NADPH. A high extent of binding to heat-inactivated microsomes indicated that no enzymic metabolic step was involved. 3. The irreversible binding of [2,3-14C]acrylonitrile to rat liver microsomal protein in vitro was inhibited by thiols (cysteine, glutathione, mercaptoethanol). The greatest inhibitory potency was displayed by dithiocarb (diethyl dithiocarbamate).

The uptake of potassium dichromate in the isolated perfused rat liver was almost complete after one hour of perfusion. No significant sex differences in chromium distribution were observed. At the end of the experiments (one hour), about 60% of the applied Cr(VI) dose (312 micrograms Cr/liver) was located in the cytosol, 14% was in the mitochondria, 9% in the microsomal pellet and 2% was associated with the nuclei. Gel chromatography of the cytosol showed that most of the chromium was in fractions with an apparent molecular weight of 6000 Da and absorption maxima at 410 nm and 548 nm. Similar optical properties and molecular weight are characteristic of GSH-Cr complexes formed by reaction of Cr(VI) with GSH in vitro.

1. [2,3-14C]Acrylonitrile was incubated with rat-liver microsomes, NADPH and either DNA, RNA or bovine serum albumin. Irreversible binding occurred to the macromolecular targets. Binding was lower when incubations were performed without microsomes. 2. Most of the 14C bound to DNA, RNA or polynucleotides (poly-A, poly-C, poly-G, poly-U) after incubation of [2,3-14C]acrylonitrile with rat-liver microsomes and 'conventional' re-isolation of the nucleic acids was removed from the macromolecular target when subsequently chromatographed on hydroxyapatite. 3. Radioactivity attached to DNA after prolonged non-enzymic incubations with [2,3-14C]acrylonitrile was also removed from the DNA by chromatography on hydroxyapatite. 4. When [2,3-14C]acrylonitrile was administered to rats (i.p.), incorporation of 14C into the natural bases of hepatic RNA was observed. In contrast with previous experiments with [1,2-14C]vinyl chloride, no radioactive [1-N6]etheno-adenine could be detected in RNA. 5. After administration of [2,3-14C]acrylonitrile to rats, hepatic DNA was isolated and hydrolysed by a modified enzymic procedure. Chromatography on PEI-cellulose showed two 14C peaks which did not co-chromatograph with any known standard. The amount of 14C in these presumed alkylation products was too low to allow chemical identification. 6. It is concluded that acrylonitrile, either itself or its metabolites, can alkylate nucleic acids. However, the extent of irreversible nucleic-acid binding is quantitatively much less than that observed with vinyl halides.

1. Oxidation of estradiol and ethynylestradiol at ring A and ring B by rat liver microsomes and NADPH-regenerating system in vitro is inhibited by the two arylimidazole insecticide synergists, 3-bromophenyl-4(5)-imidazole and 1-naphthyl-4(5)-imidazole, but not by the benzothiadiazole insectide synergists 6-nitro-1,2,3-benzothiadiazole and 5,6-dimethyl-1,2,3-benzothiadiazole. The Ki of the most potent inhibitor, 1-naphthyl-4(5)-imidazole, was 3 X 10(-6) M. 2. 6-Nitro-1,2,3-benzothiadiazole (10(-6) M), which did not inhibit hydroxylation of the estrogens, inhibited oxidation of aniline and demethylation of ethylmorphine, p-nitroanisole, and aminopyrine by 30-70%. 5,6-Dimethyl-1,2,3-benzothiadiazole inhibited only demethylation of p-nitroanisole and aminopyrine. From these results the presence of different hepatic microsomal mixed function oxidases may be inferred. 3. 1-Naphthyl-4(5)-imidazole, the most potent inhibitor of hydroxylation of drugs and estrogen rings A and B, also inhibited microsomal estrogen-16alpha-hydroxylation. 4. These data show that insecticide synergists may effect the breakdown of estrogenic hormones in the organism.

1. When [3H]rifampicin is incubated with rat liver microsomes or rat liver homogenate, minor amounts are bound irreversibly to protein. This effect does not depend on the presence of NAD, NADH, NADP or NADPH. 2. Rifampicin is autoxidized at physiological pH. The product of autoxidation, rifampicin-quinone, if incubated with albumin, shows a much greater irreversible binding to the protein than the parent compound rifampicin. Hence it is concluded that rifampicin may bind irreversibly to proteins in a non-enzymic reaction after autoxidation to rifampicin-quinone. 3. Rifampicin-quinone also binds irreversibly to RNA and poly-L-lysine, if incubated with these compounds. This suggests that free amino groups of protein or RNA are involved in the binding. 4. 48 h after dosage of [3H]rifampicin (33 mg/kg) to rats, 29-2 +/- 4-1 (S.D.) pmol are bound irreversibly to 1 mg liver RNA, 15.8 +/- 8-1 pmol to 1 mg liver protein and 5-0 +/- 0-47 pmol to 1 mg protein in brain tissue. 5. Microsomal NADPH-cytochromcin-quinone to rifampicin. The KM of this reaction is 10(-4) M. Induction of the NADPH-cytochrome c reductase by pre-treatment of rats with 20 mg/kg rifampicin over 5 days results in a corresponding increase of increase of rifampicin-quinone reduction. 6. These results suggest that microsomal NADPH-cytochrome c reductase prevents accumulation of higher amounts of possibly toxic rifampicin-quinone by reduction to rifampicin.