The potential role of topoisomerase II inhibition in hydroquinone-induced alterations in the maturation of mouse myeloblasts.
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Animals↗
Biomedical subjects
G F Kalf
Publications and source records attributed to G F Kalf.
The interaction of 1,4-benzoquinone, a bioreactive intermediate of benzene, with three proteins essential for differentiation/maturation of the mouse myeloid stem cell.
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Animals↗
Utility of a mouse model for studying the effects of benzene on the myeloid lineage: effects of hydroquinone on a model myeloid system.
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Animals↗
Hydroquinone, a bioreactive metabolite of benzene, inhibits apoptosis in myeloblasts.
Hydroquinone (a major marrow metabolite of the leukemogen, benzene) induces incomplete granulocytic differentiation of mouse myeloblasts to the myelocyte stage, and also causes an increase in the number of myelocytes. This was confirmed using the normal interleukin 3 (IL-3)-dependent mouse myeloblastic 32D cell line. The hydroquinone-induced twofold increase in the number of IL-3-treated myelocytes does not result from stimulation of IL-3-induced proliferation. Hydroquinone's ability to effect this increase through an inhibition of apoptosis was investigated using mouse 32D and human HL-60 myeloblasts. Apoptosis induced by staurosporine treatment (0.5-1.0 microM) of HL-60 cells (50%) and 32D cells (15%) or by IL-3 withdrawal from 32D myeloblasts was determined by monitoring the development of characteristic morphological features and confirmed by the appearance of a typical nucleosomal DNA ladder upon agarose gel electrophoresis. Concentrations of hydroquinone (1-6 microM) that induce differentiation in 32D myeloblasts caused a concentration-dependent inhibition of staurosporine-induced apoptosis in both cell lines, with a 50% inhibitory concentration of 3 microM, and prevented apoptosis in IL-3-deprived 32D cells. Hydroquinone inhibition of apoptosis in myeloblasts, like hydroquinone-induced granulocytic differentiation, required myeloperoxidase-mediated oxidation of hydroquinone to its reactive species, p-benzoquinone, and was inhibited 50% by the peroxidase inhibitor, indomethacin (20 microM). p-benzoquinone (3 microM) was shown to cause a 50% inhibition of CPP32, an IL-1 beta-converting enzyme/Ced-3 cysteine protease involved in the implementation of apoptosis and present in myeloid cells. The ability of hydroquinone to induce a program of differentiation in the myeloblast that proceeds only to the myelocyte stage coupled with its ability to inhibit the CPP32 protease and, thereby, apoptosis of the proliferating myelocytes, may have important implications for benzene-induced acute myeloid leukemia.
Animals↗
Benzene-induced bone marrow cell depression caused by inhibition of the conversion of pre-interleukins-1alpha and -1beta to active cytokines by hydroquinone, a biological reactive metabolite of benzene.
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Animals↗
p-Benzoquinone, a reactive metabolite of benzene, prevents the processing of pre-interleukins-1 alpha and -1 beta to active cytokines by inhibition of the processing enzymes, calpain, and interleukin-1 beta converting enzyme.
Chronic exposure of humans of benzene affects hematopoietic stem and progenitor cells and leads to aplastic anemia. The stromal macrophage, a target of benzene toxicity, secretes interleukin-1 (IL-1), which induces the stromal fibroblast to synthesize hematopoietic colony-stimulating factors. In a mouse model, benzene causes an acute marrow hypocellularity that can be prevented by the concomitant administration of IL-1 alpha. The ability of benzene to interfere with the production and secretion of IL-1 alpha was tested. Stromal macrophages from benzene-treated mice were capable of the transcription to the IL-1 alpha gene and the translation of the message but showed an inability to process the 34-kDa pre-IL-1 alpha precursor to the 17-kDa biologically active cytokine. Treatment of normal murine stromal macrophages in culture with hydroquinone (HQ) also showed an inhibition in processing of pre-IL-1 alpha. Hydroquinone is oxidized by a peroxidase-mediated reaction in the stromal macrophage to p-benzoquinone, which interacts with the sulfhydryl (SH) groups of proteins and was shown to completely inhibit the activity of calpain, the SH-dependent protease that cleaves pre-IL-1 alpha. In a similar manner, HQ, via peroxidase oxidation to p-benzoquinone, was capable of preventing the IL-1 beta autocrine stimulation of growth of human B1 myeloid tumor cells by preventing the processing of pre-IL-1 beta to mature cytokine. Benzoquinone was also shown to completely inhibit the ability of the SH-dependent IL-1 beta converting enzyme. Thus benzene-induced bone marrow hypocellularity may result from apoptosis of hematopoietic progenitor cells brought about by lack of essential cytokines and deficient IL-1 alpha production subsequent to the inhibition of calpain by p-benzoquinone and the prevention of pre-IL-1 processing.
Animals↗
Induction of granulocytic differentiation in a mouse model by benzene and hydroquinone.
Chronic exposure of humans to benzene causes acute myelogenous leukemia (AML). The studies presented here were undertaken to determine whether benzene, or its reactive metabolite, hydroquinone (HQ), affects differentiation of myeloblasts. Benzene or HQ administered to C57BL/6J mice specifically induced granulocytic differentiation of myeloblasts. The ability of these compounds to induce differentiation of the myeloblasts was tested directly using the murine interleukin 3 (IL-3)-dependent 32D.3 (G) myeloblastic cell line, and the human HL-60 promyelocytic leukemia cell line. We have previously shown that benzene treatment of HL-60 myeloblasts activates protein kinase C (PKC) and upregulates the 5-lipoxygenase (LPO) pathway for the production of leukotriene D4 (LTD4), an essential effector or granulocytic differentiation. Differentiation was prevented by sphinganine, a PKC inhibitor, and, as shown here, by LPO inhibitors and LTD4 receptor antagonists. Benzene or HQ also induces differentiation in 32D.3 (G) myeloblasts. Both compounds interact with cellular signaling pathways normally activated by granulocyte colony stimulating factor (G-CSF) and can replace the requirement for G-CSF. While IL-3 induces a growth response in 32D.3 (G) cells, G-CSF has been shown to provide both growth and differentiated signals. Both HQ and LTD4 induce differentiation and synergize with IL-3 for growth; however, neither supports growth in the absence of IL-3. Benzene, like HQ, also provides a differentiation signal for 32D cells; however, it has no effect on their growth. Unlike G-CSF, benzene, or LTD4, each of which stimulates terminal differentiation; HQ blocks differentiation at the myelocyte stage, allowing only a small percentage of progenitors to proceed to mature segmented granulocytes. Benzene- and G-CSF-induced differentiation were prevented by the additional of either LPO inhibitors or LTD4 receptor antagonists, indicating that benzene, like G-CSF, upregulates LTD4 production. Hydroquinone-induced differentiation was not affected by the LPO inhibitors, but only by the specific receptor antagonists. Thus HQ appears to obviate the requirement for LTD4 by activating the LTD4 receptor directly.
Animals↗
Inhibition of human DNA topoisomerase II by hydroquinone and p-benzoquinone, reactive metabolites of benzene.
Chronic exposure of humans to benzene (BZ) causes acute myeloid leukemia (AML). Both BZ and therapy-related secondary AML are characterized by chromosomal translocations that may occur by inappropriate recombinational events. DNA topoisomerase II (topo II) is an essential sulfhydryl (SH)-dependent endonuclease required for replication, recombination, chromosome segregation, and chromosome structure. Topo II cleaves DNA at purine(R)/pyrimidine(Y) repeat sequences that have been shown to be highly recombinogenic in vivo. Certain antineoplastic drugs stabilize topo II-DNA cleavage complexes at RY repeat sequences, which leads to translocations of the type observed in leukemia. Hydroquinone (HQ) is metabolized to p-benzoquinone (BQ) in a peroxidase-mediated reaction in myeloid progenitor cells. BQ interacts wit SH groups of SH-dependent enzymes. Consequently, the aims of this research were to determine whether HQ and BQ are topo II inhibitors. The ability of the compounds to inhibit the activity of topo III was tested using an assay system that depends on the conversion, by homogeneous human topo II, of catenated kinetoplast DNA into open and/or nicked open circular DNA that can be separated from the catenated DNA by electrophoresis in a 1% agarose-ethidium bromide gel. We provide preliminary data that indicate that both HQ and BQ cause a time and concentration (microM)-dependent inhibition of topo II activity. These compounds, which potentially can form adducts with DNA, have no effect on the migration of the supercoiled and open circular forms in the electrophoretic gradient, and BQ-adducted KDNA can be decatenated by topo II. Using a pRYG plasmid DNA with a single RY repeat as a cleavage site, it was determined that BQ does not stimulate the production of linear DNA indicative of an inhibition of topo II religation of strand breaks by stabilization of the covalent topo III-DNA cleavage complex. Rather, BQ most probably inhibits the SH-dependent topo II by binding to an essential SH group. The inhibition of topo II by BQ has implications for the formation of deleterious translocations that may be involved in BZ-induced initiation of leukemogenesis.
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Induction of granulocytic differentiation in myeloblasts by hydroquinone, a metabolite of benzene, involves the leukotriene D4 receptor.
Chronic exposure of humans to benzene (BZ), a Class I carcinogen, causes acute myelogenous leukemia, possibly via its bone marrow metabolite, hydroquinone (HQ). The ability to alter cytokine-dependent growth and differentiation in hematopoietic stem or progenitor cells appears to be a property of agents with leukemogenic potential. We have previously reported that BZ and HQ specifically stimulate granulopoiesis in mice and cause granulocytic differentiation in normal murine interleukin (IL)-3-dependent, granulocyte colony-stimulating factor (G-CSF)-inducible 32D myeloblasts. BZ induces granulocytic differentiation by upregulating the production of leukotriene D4 (LTD4), an essential intracellular mediator of G-CSF signaling. We report here that HQ (0.5-4.0 microM), as well as LTD4 (1 nM-10 microM), causes a concentration-dependent induction of granulocytic differentiation in 32D myeloblasts. Unlike LTD4, which induces terminal granulocytic differentiation, HQ undergoes a myeloperoxidase-dependent oxidation to bioreactive p-benzoquinone (BQ), which induces differentiation predominantly to the myelocyte stage. Studies with the highly specific LTD4 receptor antagonist, MK-571, suggest that BQ induces granulocytic differentiation in myeloblasts by activating the LTD4 receptor, thus obviating the requirement for LTD4. This was confirmed by the demonstration that HQ, in the presence of LTD4, shifts the stage-specific pattern of terminal differentiation induced by LTD4 to the incomplete (myelocyte) profile induced by HQ. The inability of HQ to induce a complete program of terminal granulocytic differentiation in myeloblasts, as well as its ability to compete with induction by LTD4, may have a bearing on the leukemogenic potential of BZ.
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Induction of granulocytic differentiation in myeloblasts by 17-beta-estradiol involves the leukotriene D4 receptor.
17-beta-Estradiol (beta E) causes granulocytic differentiation and neutrophilia in mice. However, the presence of estrogen receptors in myeloblasts and granulocytic progenitor cells has not been reported. beta E can be converted to a bioreactive species, estradiolquinone. We have previously shown that hydroquinone (HQ), via conversion to bioreactive p-benzoquinone (BQ), causes neutrophilia in mice and induces granulocytic differentiation in myeloblasts through interaction with the leukotriene D4 (LTD4) receptor. Therefore, we tested whether beta E could be oxidized by a myeloperoxidase-mediated reaction to a bioreactive intermediate, which might, in turn, induce granulocytic differentiation in mouse myeloblasts by activating the LTD4 receptor, thus obviating the need for LTD4, the downstream intracellular mediator of granulocyte colony-stimulating factor (G-CSF)-induced signal transduction. The interleukin (IL)-3-dependent, G-CSF-inducible normal mouse myeloblastic cell line, 32D cl 3(G), was used to determine the ability of beta E to induce terminal granulocytic differentiation in myeloblasts. Morphological analysis of stage-specific granulocytic differentiation indicated that beta E was capable of the concentration- (10(-8)-10(-4)M) and time-(6d) dependent induction of a complete program of terminal granulocytic differentiation in myeloblasts similar to that seen with G-CSF or LTD4. beta E-induced granulocytic differentiation was prevented by the peroxidase inhibitor, indomethacin, and was completely and competitively inhibited in the presence of a specific LTD4 receptor antagonist, MK-571, suggesting that a bioreactive form of estradiol, such as estradiolquinone, is interacting with the receptor. beta E was shown to cause a similar concentration-dependent induction of granulocytic differentiation in human HL-60 myeloblasts that was also inhibited by the receptor antagonist. Biological effects of beta E in nontarget tissues may result from the interaction of bioreactive estradiolquinone with critical cellular macromolecules involved in normal cellular signaling pathways.
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Inhibition of the conversion of pre-interleukins-1 alpha and 1 beta to mature cytokines by p-benzoquinone, a metabolite of benzene.
Chronic exposure of humans to benzene causes severe bone marrow cell depression leading to aplastic anemia. Marrow stromal macrophage dysfunction and deficient interleukin-1 production has been reported for patients with severe aplastic anemia. The stromal macrophage, a target of benzene toxicity, is involved in hematopoietic regulation through the synthesis of several cytokines including interleukin-1, which is required for production by stromal fibroblasts of a number of cytokines required for the survival of hematopoietic progenitor cells. We have previously demonstrated that hydroquinone, a major toxic metabolite of benzene in marrow, prevents the proteolytic conversion of 31 kDa pre-interleukin-1 alpha to the 17 kDa cytokine by calpain in purified murine stromal macrophages. Furthermore, stromal macrophages from benzene-treated mice produce the 31 kDa pre-interleukin-1 alpha when stimulated in culture with endotoxin, but cannot convert the precursor to interleukin-1 alpha. In this report, we show that 1,4-benzoquinone, the oxidation product of hydroquinone in the cell, causes a concentration-dependent inhibition of highly purified human platelet calpain with an IC50 of 3 microM. Hydroquinone also inhibits the processing of pre-interleukin-1 beta by interleukin-1 beta convertase. The addition of 2 microM hydroquinone to B1 cells that undergo autocrine stimulation by interleukin-1 beta resulted in the cessation of autocrine cell growth and interleukin-1 beta secretion into the culture medium, as determined by Western immunoblots of the culture supernatants. Purified converting enzyme treated with 3 microM benzoquinone was incapable of converting 31 kDa recombinant pre-interleukin-1 beta to the 17 kDa mature cytokine as analyzed by polyacrylamide gel electrophoresis and Western immunoblotting. These findings support our observations in a mouse model that benzene-induced bone marrow cell depression results from a lack of interleukin-1 alpha subsequent to an inhibition by benzoquinone of calpain, the protease required for converting pre-interleukin-1 alpha to active cytokine. The results may provide a basis for studying benzene-induced aplastic anemia in a mouse model.
Benzene↗
Benzene and its metabolite, hydroquinone, induce granulocytic differentiation in myeloblasts by interacting with cellular signaling pathways activated by granulocyte colony-stimulating factor.
Chronic exposure of humans to benzene (BZ) causes acute myelogenous leukemia. These studies determined whether BZ, or its reactive metabolite, hydroquinone (HQ), affect differentiation of myeloblasts. BZ or HQ administered to C57BL/6J mice specifically induced terminal granulocytic differentiation of myeloblasts. The ability of the compounds to induce differentiation of the myeloblast was tested directly using the murine interleukin 3 (IL-3)-dependent myeloblastic cell line, 32D.3 (G) and the human HL-60 promyelocytic leukemic cell line. Treatment of HL-60 myeloblasts with BZ activated protein kinase C and upregulated the 5-lipoxygenase (LPO) pathway for the production of leukotriene D4 (LTD4), an essential effector of granulocytic differentiation. Differentiation was prevented by sphinganine, a kinase C inhibitor, as well as by LPO inhibitors and LTD4 receptor antagonists. BZ and HQ also induced differentiation in 32D.3 (G) myeloblasts. Both compounds interact with cellular signaling pathways activated by granulocyte colony-stimulating factor (G-CSF) and thus replace the requirement for G-CSF. IL-3 induces a growth response, whereas G-CSF provides both growth and differentiation signals. BZ does not induce growth in the absence of IL-3, but provides a differentiation signal. Both HQ and LTD4 induce differentiation and synergize with IL-3 for growth, however, neither support growth in the absence of IL-3. BZ-induced 32D cells showed a gradual progression of progenitor differentiation to granulocytes similar to that seen with G-CSF or LTD4. HQ blocks differentiation at the myelocyte stage; only a small percentage of progenitors proceed to granulocytes. BZ, like G-CSF, upregulates LTD4 production, whereas HQ obviates the requirement for LTD4 by activating the LTD4 receptor.
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A morphological analysis of the short-term effects of benzene on the development of the hematological cells in the bone marrow of mice and the effects of interleukin-1 alpha on the process.
Chronic exposure of humans to benzene (BZ), a widely used industrial chemical and a ubiquitous environmental pollutant, causes aplastic anemia and acute myeloid leukemia. The purpose of the studies reported here was to determine whether the observed depression of bone marrow (BM) cellularity in mice administered benzene was reflected in a suppression of development of all of the hematopoietic lineages and to confirm the ability of interleukin-1 alpha (IL-1 alpha) to prevent BZ-induced BM cell depression. We report that BZ, administered twice per day for 2 days to C57B1/6J mice at a dose of 600 mg/kg body weight, caused a significant depression of the total number of nucleated BM cells per femur when measured on day 3. The observed depression reflects a complex situation that represents the net effect of a decrease in the total number of cells of the lymphocytic and erythroid lineages, along with an increase in the number of intermediate and terminally differentiated cells of the granulocytic lineage. An experiment to monitor the effects of BZ over a 7-day period showed a progressive depressive effect on the lymphocytes and an initial depression of the erythroid cells at day 3 that remained constant until day 7. Conversely, the numbers of intermediate and terminally differentiated granulocytes progressively increased over the 7 days. The BM appeared to recover from the depressive effects of BZ immediately upon cessation of exposure, as the number of nucleated BM cells began to rise by day 5 and was equal to that of the control group by day 7. The results expand our earlier finding (Renz and Kalf 1991) that the overall depression of BM cellularity occurs because of an inability of the stromal fibroblast to produce colony-stimulating factors essential for stem and progenitor cell survival. This results from inhibition by the BZ metabolite, hydroquinone (HQ), of the processing of pre-IL-1 alpha to the mature cytokine.(ABSTRACT TRUNCATED AT 250 WORDS)
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A perspective on benzene leukemogenesis.
Although benzene is best known as a compound that causes bone marrow depression leading to aplastic anemia in animals and humans, it also induces acute myelogenous leukemia in humans. The epidemiological evidence for leukemogenesis in humans is contrasted with the results of animal bioassays. This review focuses on several of the problems that face those investigators attempting to unravel the mechanism of benzene-induced leukemogenesis. Benzene metabolism is reviewed with the aim of suggesting metabolites that may play a role in the etiology of the disease. The data relating to the formation of DNA adducts and their potential significance are analyzed. The clastogenic activity of benzene is discussed both in terms of biomarkers of exposure and as a potential indication of leukemogenesis. In addition to chromosome aberrations, sister chromatid exchange, and micronucleus formation, the significance of chromosomal translocations is discussed. The mutagenic activity of benzene metabolites is reviewed and benzene is placed in perspective as a leukemogen with other carcinogens and the lack of leukemogenic activity by compounds of related structure is noted. Finally, a pathway from exposure to benzene to eventual leukemia is discussed in terms of biochemical mechanisms, the role of cytokines and related factors, latency, and expression of leukemia.
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The effects of benzene and hydroquinone on myeloid differentiation of HL-60 promyelocytic leukemia cells.
Chronic exposure of humans to benzene (BZ) affects hematopoietic progenitor cells in intermediate stages of differentiation which can lead to aplastic anemia and/or acute myelogenous leukemia and some of its variant forms. We studied the effects of BZ and hydroquinone (HQ), a toxic bone marrow metabolite, on the human HL-60 promyelocytic leukemic cell line. Because the HL-60 cell is bipotential and can be induced to differentiate to monocytes or granulocytes it has been used in many studies as a surrogate for the granulocyte/macrophage committed cell, GM-CFU. Treatment of HL-60 cells with BZ specifically induced differentiation along the granulocytic lineage as measured by morphology, induction of superoxide production and chloroacetate esterase activity and the appearance of the L12-2 surface antigen. Differentiation was induced via the activation of protein kinase C and the phosphorylation of several proteins known to be involved in HL-60 cell differentiation. Subsequent to kinase C activation, arachidonic acid was released from membrane phospholipids and the 5-lipoxygenase pathway was activated for the production of leukotriene D4 (LTD4) required for granulocytic differentiation. BZ induction of granulopoiesis was prevented by preincubation of HL-60 cells with inhibitors of protein kinase C, 5-lipoxygenase, gamma-glutamyl transpeptidase required for the conversion of LTC4 to LTD4, or LTD4 receptor antagonists. Treatment of HL-60 cells with tetraphorbol myristate acetate (TPA), 1 alpha, 25-dihydroxyvitamin D3 (1,25-(OH2)D3) or interleukin-1 (IL-1) induced HL-60 cells to differentiate to monocytes/macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)
Arachidonate 5-Lipoxygenase↗
Induced differentiation of HL-60 promyelocytic leukemia cells to monocyte/macrophages is inhibited by hydroquinone, a hematotoxic metabolite of benzene.
Chronic exposure of humans to benzene has been shown to have a cytotoxic effect on hematopoietic progenitor cells in intermediate stages of differentiation, which can lead to aplastic anemia and acute myelogenous leukemia. We studied the effect of hydroquinone (HQ), a toxic metabolite of benzene found in the bone marrow, on the human promyelocytic leukemia cell line (HL-60), which can be induced to differentiate to both monocyte and myeloid cells, and thus has been used as a surrogate for a granulocyte/macrophage progenitor cell. Exposure of HL-60 cells to noncytotoxic concentrations of HQ for 3 hours before induction with phorbol myristate acetate (TPA) caused a dose-dependent inhibition of the acquisition of characteristics of monocytic differentiation, such as adherence, nonspecific esterase (NSE) activity, and phagocytosis, but had no effect on cell proliferation. HQ appeared to be affecting maturation beyond the monoblast/promonocyte stages. HQ also prevented differentiation induced by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]; however, the block occurred after the acquisition of adherence. HQ at concentrations that inhibited monocytic differentiation had no effect on differentiation to granulocytes, suggesting that the block in the differentiation of these bipotential cells is a step unique to the monocytic pathway. HQ was unable to prevent differentiation induced by the macrophage-derived cytokine, interleukin (IL)-1, a differentiation factor for cells of the monocytic lineage.
Benzene Derivatives↗
Role for interleukin-1 (IL-1) in benzene-induced hematotoxicity: inhibition of conversion of pre-IL-1 alpha to mature cytokine in murine macrophages by hydroquinone and prevention of benzene-induced hematotoxicity in mice by IL-1 alpha.
Chronic exposure of humans to benzene (BZ), a myelotoxin, causes aplastic anemia and acute leukemia. The stromal macrophage that produces interleukin-1 (IL-1), a cytokine essential for hematopoiesis, is a target of BZ's toxicity. Monocyte dysfunction and decreased IL-1 production have been shown to be involved in aplastic anemia in humans. Hydroquinone (HQ), a toxic bone marrow (BM) metabolite of BZ, causes time- and concentration-dependent inhibition of processing of the 34-Kd pre-interleukin-1 alpha (IL-1 alpha) to the 17-Kd mature cytokine in murine P388D1 macrophages and BM stromal macrophages, as measured by Western immunoblots of cell lysate proteins using a polyclonal rabbit antimurine IL-1 alpha antibody. HQ over a 10-fold concentration range had no effect on the lipopolysaccharide (LPS)-induced production of pre-IL-1 alpha precursor or on cell viability or DNA and protein synthesis. Stromal macrophages obtained from the femoral BM of C57Bl/6 mice exposed to BZ (600 or 800 mg/kg body weight) for 2 days were incapable of processing the 34-Kd pre-IL-1 alpha to the mature 17-Kd cytokine when stimulated in culture with LPS. Stromal macrophages from mice coadministered BZ and indomethacin, a prostaglandin H synthase (PHS) inhibitor that has been shown to prevent BZ-induced myelotoxic and genotoxic effects in mice when coadministered with benzene were able to convert the pre-IL-1 alpha to mature cytokine. Administration of recombinant murine IL-1 alpha (rMuIL-1 alpha) to mice before a dose of BZ that causes severe depression of BM cellularity completely prevents BM depression, most probably by bypassing the inability of the stromal macrophage in BZ-treated animals to process pre-IL-1 alpha to the mature cytokine.
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Purification and characterization of a benzene hydroxylase from rat liver mitochondria.
An enzyme has been purified to electrophoretic homogeneity from rat liver mitoplasts which metabolizes benzene to phenol. The enzyme has a Mr of 52,000 and requires NADPH, adrendoxin, and adrenodoxin reductase for activity. Benzene hydroxylase activity could be inhibited by carbon monoxide and SKF-525A, and by specific inhibitors of microsomal benzene metabolism. The purified enzyme also oxidized phenol to catechol. The data suggest that a cytochrome P-450 of mitochondrial origin is involved in benzene metabolism, and provide another example of a role for the mitochondrion in xenobiotic activation.
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