Cytochrome a1c1 (nitrite-cytochrome c oxidoreductase) purified from Nitrobacter winogradskyi (formerly N. agilis) contained molybdenum, non-heme iron, and acid-labile sulfur in addition to hemes a and c; it contained 1 mol of heme a, 4-5 g atoms of non-heme iron, 2-5 g atoms of acid-labile sulfur, and 1-2 g atoms of molybdenum per mol of heme c, but did not contain copper. The fluorescence spectra of the molybdenum cofactor derivative prepared from cytochrome a1c1 were very similar to those of the cofactor derivative from xanthine oxidase, and the aponitrate reductase of nit-1 mutant of Neurospora crassa was complemented by addition of the molybdenum cofactor derived from the cytochrome. Further, the ESR spectrum of cytochrome a1c1 was similar to that of liver sulfite oxidase. The content of cytochrome a1 in the cells cultivated with the medium in which tungsten was substituted for molybdenum markedly decreased as compared with that in the cells cultivated in the molybdenum-supplemented medium. These results indicate that cytochrome a1c1 is an iron-sulfur molybdoenzyme which contains hemes a and c.

The influence of the amount and type of dietary lipid on rat hepatic cytochrome P-450 activities in the presence and absence of inducer administration was investigated. Weanling male Sprague-Dawley rats were fed fat-free or 20% beef tallow, olive oil, corn oil, linseed oil, or menhaden oil diets in combination with one of the following three treatments: no inducer, intraperitoneal injection of phenobarbital (75 mg/kg body wt) for three consecutive days before they were killed, or intragastric administration of acetone (5 ml/kg) one day before they were killed. Twenty percent linseed oil and menhaden oil diets induced the highest level of activity among the different fat types in the presence of phenobarbital and acetone. Cytochrome P-450IIB1 activity was induced to a significantly greater extent by acetone administration in conjunction with the 20% menhaden oil diet than in conjunction with the other dietary oils (p < 0.05). In the presence of acetone, 20% beef tallow, 20% linseed oil, and 20% menhaden oil diets significantly induced cytochrome P-450IIE1 activity compared with the fat-free diet (p < 0.05). In conclusion, cytochrome P-450IIB1 and P-450IIE1 activities in rats were significantly increased by specific inducers, and dietary lipid was necessary for this effect. Diets supplemented with linseed and menhaden oils were most effective in inducing this activity.

J Biol Inorg Chem 1999 Apr;4(2):145-53

National Research Centre for Environmental Toxicology, University of Queensland, Australia.

Copper is an absolute requirement for living systems and the intracellular trafficking of this metal to copper-dependent proteins is fundamental to normal cellular metabolism. The copper chaperones perform the dual functions of trafficking and the prevention of cytoplasmic exposure to copper ions in transit. Only a small number of copper chaperones have been identified at this time but their conservation across plant, bacterial and animal species suggests that the majority of living systems utilise these proteins for copper routing. The available data suggest that each copper-dependent protein in the cell is served by a specific copper chaperone. Although copper chaperones cannot be substituted for one another in a given cell type, copper chaperones that deliver to the same protein in different cell types appear to be functionally equivalent. The majority of the copper chaperones identified thus far have an "open-faced beta-sandwich" global fold with a conserved MXCXXC metal-binding motif. Specificity for a given copper-dependent protein appears to be mediated by the residues surrounding the copper-binding motif. Copper binds to such proteins as Cu(I) in a trigonal complex with three sulfur ligands. Only the copper chaperone specific for cytochrome-c-oxidase, Cox17, deviates from this design.

Male rats are the most frequently used experimental animals in drug toxicity tests. However, there are clear sex-related differences in toxicity of various drugs and chemicals in rats. These differences, in most cases, are closely connected with the sex-related differences in hepatic drug metabolisms. Recent studies indicate the existence of sex-specific cytochrome P450, such as P450-male (2C11) and P450-female (2C12) and P450(6) beta (3A2) in rat livers, and also show that their expression levels are markedly different between male and female rats. The expressions of sex-specific P450s are regulated by growth hormone, thyroid hormone, sex hormones and other chemicals. On the other hand, there are no or few cytochrome P450s that show the sex-related differences in species other than rats and mice. Although there are orthologous cytochrome P450s in viewpoints of amino acid sequence and substrate specificity in experimental animal species and humans, their expressions are not regulated by hormonal factors in most of the species. These differences may cause clear species differences, if male animals are used, in the toxicity caused by various drugs and chemicals. Thus we can predict the sex-related difference in drug toxicity on the basis of difference in the expression levels of sex-specific cytochrome P450s.

Title

Cytochrome c reduction by triiodothyronine (T3).

Author

Peterson DA

Source

Med Hypotheses, 9(1):111-4 1982 Jul

Abstract

Triiodothyronine (T3), the active thyroid hormone, reduced cytochrome c non-enzymatically. This reduction was partially inhibited by superoxide dismutase (SOD). Thyroxine (T4) was only minimally effective as a reductant in this system. The effect of T3 on mitochondrial oxidative phosphorylation may involve a direct redox mechanism.

Title

Role of xanthine oxidase in the interferon-mediated depression of the hepatic cytochrome P-450 system in mice.

Author

Mannering GJ; Deloria LB; Abbott V

Address

Department of Pharmacology, University of Minnesota Medical School, Minneapolis 55455.

Source

Cancer Res, 48(8):2107-12 1988 Apr 15

Abstract

Interferon, interferon inducers, and a variety of other immunomodulators are known to depress the hepatic cytochrome P-450 drug-metabolizing system. Two concepts have been proposed to explain this phenomenon. (a) The steady-state of cytochrome P-450 is altered through decreased synthesis and increased degradation of cytochrome P-450 apoprotein. (b) Interferon induces xanthine oxidase; superoxide generated by interferon-induced xanthine oxidase destroys cytochrome P-450. The current study investigated the second concept. Administered polyribonucleotides [polyriboinosinic acid.polyribocytidylic acid (poly IC), polyriboinosinic acid.polycytidylic acid, polylysine and carboxymethylcellulose, mismatched poly IC], recombinant murine gamma-interferon, and a natural murine alpha/beta-interferon were shown to depress hepatic cytochrome P-450 and selected microsomal cytochrome P-450-dependent monooxygenase reactions and to induce hepatic xanthine oxidase activity. The feeding of tungstate in the drinking water largely depleted xanthine oxidase in mice; cytochrome P-450 levels and monooxygenase activities were not affected by tungstate treatment. Tungstate rendered the level of xanthine oxidase much below that in mice that had not received tungstate regardless of whether or not they had received poly IC or interferon; nevertheless, poly IC and interferon produced losses of cytochrome P-450 and monooxygenase activities in these tungstate-treated mice equivalent to those observed in mice that had not received tungstate. The administration of N-acetylcysteine did not prevent the loss of cytochrome P-450 induced by poly IC, as has been reported, nor did the incubation of microsomal cytochrome P-450 with buttermilk xanthine oxidase and hypoxanthine cause a loss of cytochrome P-450, which has also been reported. It is concluded from these studies that the induction of xanthine oxidase and the loss of cytochrome P-450 generated by interferon are coincidental rather than causally related phenomena.