UDP-glucosyltransferase activity of housefly microsomal fraction

Housefly UDP-glucosyltransferase activity towards p-nitrophenol was demonstrated in a system in vitro. The activity is localized in the microsomal fraction, requires UDP-glucose, is slightly stimulated by Mg2+ and is activated optimally over a wide range of detergent concentration. Phenobarbital increases the enzyme(s) activity about 3-fold, with p-nitrophenol as substrate, which differs from the corresponding mammalian glucuronyltransferase.

Fate of juvenile hormone in mammalian cell culture

The metabolism of juvenile hormone (JH) I has been examined in fetal mouse liver cells maintained in culture. Diffusion of the hormone into the cells appears to be passive. The hormone is metabolized essentially to organic-soluble metabolites (diol ester, diol acid and acid) by the action of epoxide hydrase and carboxylesterases. Conjugative reactions play a minor role, less than 3% of the hormone being excreted as conjugates (glucuronides, sulfates and mercapturic acid). About 0.8% of the cellular radioactivity is bound to macromolecules, mainly those of nuclear and mitochondrial origin. Metyrapone and SKF 525-A inhibit covalent binding of the hormone to cytoplasmic macromolecules, which suggests participation of the cytochrome P-450 system in covalent binding of the hormone.

Cytochrome P-450 and hydroxylating activity of microsomal preparations from whole houseflies

1. A new microsomal preparation, obtained from whole houseflies is described in terms of its cytochrome P-450 content and its hydroxylating activity. 2. Microsomes prepared from whole-fly brei, obtained with the aid of a mortar (a procedure that avoids the destruction of sarcosomes), contain 0.265nmol of cytochrome P-450 and hydroxylate naphthalene at a rate of 28.5nmol/mg of microsomal protein in 30min at 30 degrees C. This corresponds to 104nmol of naphthalene hydroxylated/nmol of cytochrome P-450. This is the highest rate ever reported for housefly and rat liver microsomal preparations. 3. Microsomal fractions prepared by procedures that do not retain the integrity of sarcosomes show the presence in the CO-difference spectrum of a 428nm peak. This cytochrome is associated with sarcosomal microsomes and it may be involved in the inhibition of insect microsomal mixed-function oxidases, although other factors cannot be discarded at present. 4. The inability to show cytochrome P-450 in microsomal fractions isolated from whole houseflies by other procedures may be at least partially due to a masking effect brought about by contamination with the sarcosomal cytochrome.

Mechanism of detoxication of some organophosphorus compounds: the role of glutathione-dependent demethylation

The detoxication of the geometrical isomers of Bomyl® (dimethyl-1,3-dicarbomethoxy-1-propen-2-yl phosphate) and Phosdrin® (mevinphos, dimethyl-1-carbomethoxy-1-propen-2-yl phosphate) by mouse liver has been studied. Most of the degrading activity for Phosdrin isomers was found in the supernatant fraction, whereas for Bomyl isomers it was equally distributed between the microsomal and the supernatant fractions. cis-Phosdrin is degraded in a system which requires reduced glutathione, the metabolites being cis-monomethyl-1-carbomethoxy-1-propen-2-yl phosphate (cis-desmethyl-Phosdrin)and S-methylglutathione. On the other hand, tras-Phosdrin and both Bomyl isomers were degraded to dimethyl phosphate. A method for the synthesis of cis-thiono-Bomyl is also reported. The possible general role of glutathione in the degradation of organophosphorus compounds is discussed.