Metabolic activation of 3-methylcholanthrene: mutagenic and transforming activities of the 9,10-dihydrodiol.

3-Methylcholanthrene and five related dihydrodiols have been tested for microsome-mediated mutagenicity towards $\text{Salmonella}\text{typhimurium}$ TA100 and for the induction of mutation to 8-azaguanine resistance in V79 Chinese hamster cells and malignant transformation in M2 mouse fibroblasts. In both mutagenicity test systems, the 9,10-diol was considerably more active than either the parent hydrocarbon, the related $\text{cis}$-2α,3-diol, the $\text{trans}$-4,5-, the $\text{trans}$-7,8- or the $\text{trans}$-11,12-dihydrodiols. At a non-toxic concentration (1μg/ml medium), the 9,10-diol induced the formation of more transformed malignant foci in cultures of M2 cells than 3-methylcholanthrene and the other diols were either inactive or only weakly active in this test system. The results obtained indicate that the 9,10-dihydrodiol derived from 3-methylcholanthrene is involved, presumably following conversion into the corresponding vicinal diol-epoxide, 9,10-dihydro-9,10-dihydroxy-3-methylcholanthrene 7,8-oxide, in the metabolic activation of this carcinogenic polycyclic hydrocarbon.     

Benzo[a]pyrene-7,8-dihydrodiol: selective binding to single stranded DNA and inactivation of 0X174 DNA infectivity.

When single-stranded ØX174 DNA is exposed to certain dihydrodiol derivatives of benzo[a]pyrene and benz[a]anthracene, inhibition of viral DNA infectivity is observed. Binding studies with labeled $\text{trans}$-7,8-dihydrodiol of benzo[a]pyrene and $\text{anti}$-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide indicate that the diol preferentially reacts with single-stranded DNA, whereas the diolepoxide reacts equally well with both single- and double-stranded DNA, as well as with RNA. Also, the diol and diolepoxide derivatives show a marked difference in their capacity to complex with specific deoxyhomopolymers, i.e., Poly dI. These observations suggest that the diol and diolepoxide derivatives recognize different binding sites in nucleic acids, and that the diol derivative may play an important role in mutagenesis and carcinogenesis induced by polycyclic aromatic hydrocarbons.     

Formation of 9,10-epoxypalmitate and 9,10-dihydroxypalmitate from palmitoleic acid by a soluble system from Bacillus megaterium.

A soluble, cytochrome P-450-containing system from $\text{Bacillus}\text{megaterium}$ which catalyzes the monohydroxylation of long-chain saturated fatty acids has now been found to convert palmitoleic acid to 9,10-epoxypalmitate and 9,10-dihydroxypalmitate in addition to the expected isomeric mixture of monohydroxypalmitoleic acids.     

Structure elucidation of a 6-methylbenzo[a]pyrene-DNA adduct formed by horseradish peroxidase in vitro and mouse skin in vivo

Activation of polycyclic aromatic hydrocarbons (PAH) by horseradish peroxidase (HRP) with H₂O₂ has been studied as a model system for one-electron oxidation. This peroxidase has been used to catalyze binding of $\text{6-}\text{[}{}^{14}\text{C]methylbenzo}\text{[a]}\text{pyrene}$ (BP-6-CH₃) to DNA, which was purified, hydrolyzed to deoxyribonucleosides and analyzed by high pressure liquid chromatography (HPLC). The predominant hydrocarbon-DNA adduct observed was identified as BP-6-CH₃ bound at the 6-methyl group to the 2-amino group of dG, confirming that activation by HRP occurs by one-electron oxidation. When DNA from mouse skin treated in vivo with [¹⁴C]BP-6-CH₃ was purified, hydrolyzed and analyzed by HPLC, a profile was observed which was qualitatively similar to that from the peroxidase system. In particular, the identified adduct with the hydrocarbon bound at the 6-methyl group to the 2-amino group of dG was obtained. These results demonstrate that one-electron oxidation is the mechanism of activation by HRP for aromatic hydrocarbons and indicate that the same mechanism may occur in mouse skin, a target tissue for hydrocarbon carcinogenesis.     

High mutagenicity and toxicity of a diol epoxide derived from benzo[a]pyrene

(±)-7β,8α-Dihydroxy-9β,10β-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BP 7,8-diol-9,10-epoxide) is a suspected metabolite of benzo[a]pyrene that is highly mutagenic and toxic in several strains of $\text{Salmonella}\text{typhimurium}$ and in cultured Chinese hamster V79 cells. BP 7,8-diol-9,10-epoxide was approximately 5, 10 and 40 times more mutagenic than benzo[a]pyrene 4,5-oxide (BP 4,5-oxide) in strains TA 98 and TA 100 of $\text{S.}\text{typhimurium}$ and in V79 cells, respectively. Both compounds were equally mutagenic to strain TA 1538 and non-mutagenic to strain TA 1535 of $\text{S.}\text{typhimurium}$. The diol epoxide was toxic to the four bacterial strains at 0.5–2.0 nmole/plate, whereas BP 4,5-oxide was nontoxic at these concentrations. In V79 cells, the diol epoxide was about 60-fold more cytotoxic than BP 4,5-oxide.     

Antimicrobial activity of juncusol, a novel 9-10-dihydrophenanthrene from the marsh plant Juncus roemerianus

The 9,10-dihydrophenanthrene phenolic compound juncusol, from the marsh plant $\text{Juncus}$$\text{roemerianus}$, has been shown to be inhibitory to four species of naturally occurring $\text{Bacillus}$ and to two ATCC species $\text{Bacillus}$$\text{subtilis}$ and $\text{Staphylococcus}$$\text{aureus}$. Juncusol may regulate populations of bacillus bacteria in the marsh and has potential as an antimicrobial agent particularly to gram positive microorganisms.     

Metabolism of cyclopenta(cd)pyrene at the K-region by microsomes and a reconstituted cytochrome P-450 system from rat liver

Liver microsomes and reconstituted cytochrome P-450 systems purified from phenobarbital or 3-methylcholanthrene pre-treated rats metabolize cyclopenta(cd)pyrene at its K-region to $\text{trans}$-9,10-dihydroxy-9,10-dihydrocyclopenta(cd)pyrene. The rate of formation of the K-region product is from 5% to 25% that of $\text{trans}$-3,4-dihydroxy-3,4-dihydro-cyclopenta(cd)pyrene. The preference of microsomes and purified cytochromes P-450 for oxygenating cyclopenta(cd)pyrene at the ethylenic C(3)–C(4) position is explainable in part by the fact that the C(4) position has the greatest electron density in the highest occupied molecular orbital.     

The non-covalent binding of benzo[a]pyrene and its hydroxylated metabolites to intracellular proteins and lipid bilayers

The non-covalent interactions of benzo[a]pyrene (BP) and several of its hydroxylated metabolites with ligandin, aminoazodye-binding protein A (Z-protein, fatty acid binding protein) and lecithin bilayers have been studied by equilibrium dialysis, an adsorption technique and fluorescence spectroscopy. Binding affinities expressed as $\text{v}\text{/c}$ (where $\text{v}$ = moles of BP or BP metabolite bound per mole of protein or lipid and c = unbound concentration), were measured at concentrations sufficiently low that there was no self-association of the unbound compounds as judged by their fluorescence characteristics. 3-Hydroxybenzo[a]pyrene (BP-3-phenol), 4,5-dihydro-4,5-dihydroxybenzo[a]pyrene (BP-4,5-dihydrodiol) and 7,8-dihydro-7,8-dihydroxybenzo[a]pyrene (BP-7,8-dihydrodiol) bind more strongly ($\text{v}\text{/c = 10}{}^5\text{?5 · 10}{}^5\text{l}\text{·}\text{mol}{}^{\mathrm{?1}}$) to all three binders than does BP itself ($\text{v}\text{/c = 10}{}^4\text{?7 · 10}{}^4\text{l}\text{·}\text{mol}{}^{\mathrm{?1}}$). 9,10-Dihydro-9,10-dihydroxybenzo[a]pyrene (BP-9,10-dihydrodiol) binds to ligandin with an affinity similar to those of the other BP metabolites studied here, but binds much less strongly to both protein A and lecithin ($\text{v}\text{/c = 10}{}^4$ and 3 · 10⁴ l · mol^?1, respectively). The low affinity of BP-9,10-dihydrodiol for lecithin would account for earlier findings that on incubation of BP with isolated rat hepatocytes, this metabolite egressed from the cells to the extracellular medium much more readily than either BP-4,5-dihydrodiol or BP-7,8-dihydrodiol.Calculations based on these results suggest that within hepatocytes BP and its metabolites, including BP-9,10-dihydrodiol, will be found almost exclusively associated (>98%) with lipid membranes.     

Fluorescence properties of a benzo(a)pyrene 7,8 dihydrodiol 9,10-oxide-DNA adduct. Conformation and effects of intermolecular DNA interactions

The pyrene-like fluorescence of the covalent benzo(a)pyrene diol-epoxide-DNA complex prepared by reacting 7,8,-dihydrodiol 9,10-epoxy benzo(a)pyrene (BPDE) with DNA in aqueous solution $\text{in vitro}$, has been investigated. It is shown that this fluorescence is $\text{sensitive}$ to molecular oxygen, to the concentration of $\text{native}$ DNA and to the ionic strength (KCl concentration), but is $\text{insensitive}$ to the concentration of $\text{denatured}$ DNA. These effects are related to the conformation of the pyrene-like chromophore of BPDE. Most of the fluorescence of a $\text{dilute}$ solution of the DNA-bound benzo(a)pyrene derivative originates from binding sites in which the pyrene moiety is not intercalated between the DNA base pairs, but is located on the outside of the DNA double helix.     

Involvement of singlet oxygen in the fungal degradation of lignin

The possible involvement of singlet oxygen (¹O₂) in the degradation of lignin by $\text{Phanerochaete}\text{chrysosporium}$ was examined. Ligninolytic cultures and photochemically generated ¹O₂ gave the same oxidation products from the lignin substructure model compound 1,2-bis(3-methoxy-4-alkoxyphenyl)propan-1,3-diol. Fluorescence and near UV absorbance of the specific ¹O₂ trapping agent anthracene-9,10-bisethanesulfonic acid (AES) disappeared in ligninolytic cultures, indicating that ¹O₂ was produced. AES strongly inhibited oxidation of ¹⁴C-lignin, but not ¹⁴C-glucose, to ¹⁴CO₂ in cultures, and also strongly suppressed oxidation of the model compound. These results indicate the ¹O₂ plays an integral role in lignin biodegradation.     

Cellular binding of benzo(a)pyrene to DNA characterized by low temperature fluorescence

A new approach has been developed to detect ultra low concentrations of benzo(a)pyrene products bound to nucleic acids $\text{in}\text{vivo}$. The binding to DNA of hamster embryo cell cultures was characterized by low temperature fluorescence spectroscopy. The method can detect less than one polycyclic hydrocarbon residue per 50,000 nucleotides. The fluorescence spectra indicate that the benzo(a)pyrene derivative bound to DNA has a pyrene-like chromophore and resembles that obtained when DNA is reacted $\text{in}\text{vitro}$ with the 7,8-diol-9,10-oxide of benzo(a)pyrene. This confirms that metabolism of the 7,8,9,10 ring on benzo(a)pyrene precedes reaction with DNA. The method should be useful for detecting and characterizing the $\text{in}\text{vivo}$ binding of other fluorescent carcinogens to nucleic acids.     

Stereoselective formation of a K-region dihydrodiol from phenanthrene by Streptomyces flavovirens

The metabolism of phenanthrene, a polycyclic aromatic hydrocarbon (PAH), by Streptomyces flavovirens was investigated. When grown for 72 h in tryptone yeast extract broth saturated with phenanthrene, the actinomycete oxidized 21.3% of the hydrocarbon at the K-region to form trans-9,10-dihydroxy-9,10-dihydrophenanthrene (phenanthrene trans-9,10-dihydrodiol). A trace of 9-phenanthrol was also detected. Metabolites isolated by thin-layer and high performance liquid chromatography were identified by comparing chromatographic, mass spectral, and nuclear magnetic resonance properties with those of authentic compounds. Experiments using [9-¹⁴C]phenanthrene showed that the trans-9,10-dihydrodiol had 62.8% of the radioactivity found in the metabolites. Circular dichroism spectra of the phenanthrene trans-9,10-dihydrodiol indicated that the absolute configuration of the predominant enantiomer was (–)-9S,10S, the same as that of the principal enantiomer produced by mammalian enzymes. Incubation of S. flavovirens with phenanthrene is an atmosphere of ¹⁸O₂, followed by gas chromatographic/mass spectral analysis of the metabolites, indicated that one atom from molecular oxygen was incorporated into each molecule of the phenanthrene trans-9,10-dihydrodiol. Cytochrome P-450 was detected in 105,000×g supernatants prepared from cell extracts of S. flavovirens. The results show that the oxidation of phenanthrene by S. flavovirens was both regio- and stereospecific.Abbreviations CD circular dichroism - DMF N,N-dimethyl-formamide - GC/MS gas chromatography/mass spectrometry - HPLC high performance liquid chromatography - NMR nuclear magnetic resonance - ODS octadecylsilane - PAH polycyclic aromatic hydrocarbon - TLC thin-layer chromatography - TMS tetramethylsilane - UV ultraviolet     

Kinetics of hydrolysis to tetraols and binding of benzo(a)pyrene-7,8-dihydrodiol-9,10-oxide and its tetraol derivatives to DNA. Conformation of adducts

When the major reactive metabolite of benzo(a)pyrene, $\text{trans}$ -7,8-dihydroxy - $\text{anti}$-9,10-epoxy -7,8,9,10-tetrahydrobenzo(a)pyrene ($\text{anti}$-BPDE) is incubated with DNA in aqueous solution at 25°C, both covalent binding and hydrolysis of $\text{anti}$-BPDE to its tetraols occur. Using fluorescence and absorption spectroscopy it is shown that hydrolysis of $\text{anti}$-BPDE is markedly accelerated by DNA. In the presence of 5A₂₆₀ units of DNA per ml in cacodylate buffer solution, at an initial concentration of DNA phosphate/$\text{anti}$-BPDE ratio of 100, both the extent of covalent binding to DNA ( < 7% of the total $\text{anti}$-BPDE initially present) and hydrolysis of $\text{anti}$-BPDE reach their maximum levels within less than five minutes after mixing. Absorption and electric linear dichroism spectra indicate that the tetraols bind non-covalently to DNA by an intercalation mechanism, whereas the covalent product displays the characteristics of an externally bound complex.     

Novel evidence of cytochrome P450-catalyzed oxidation of phenanthrene in <Emphasis Type="Italic">Phanerochaete chrysosporium</Emphasis> under ligninolytic conditions

The presence of cytochrome P450 and P450-mediated phenanthrene oxidation in the white rot fungus Phanerochaete chrysosporium under ligninolytic condition was first demonstrated in this study. The carbon monoxide difference spectra indicated induction of P450 (130 pmol mg⁻¹ in the microsomal fraction) by phenanthrene. The microsomal P450 degraded phenanthrene with a NADPH-dependent activity of 0.44 ± 0.02 min⁻¹. One of major detectable metabolites of phenanthrene in the ligninolytic cultures and microsomal fractions was identified as phenanthrene trans-9,10-dihydrodiol. Piperonyl butoxide, a P450 inhibitor which had no effect on manganese peroxidase activity, significantly inhibited phenanthrene degradation and the trans-9,10-dihydrodiol formation in both intact cultures and microsomal fractions. Furthermore, phenanthrene was also efficiently degraded by the extracellular fraction with high manganese peroxidase activity. These results indicate important roles of both manganese peroxidase and cytochrome P450 in phenanthrene metabolism by ligninolytic P. chrysosporium.     

Dominant form of cationic peroxidase from sorghum roots

A dominant form of cationic peroxidase (PO-2) was isolated from sorghum (Sorghum bicolor L. Moench) roots and purified to electrophoretically homogeneous state. The enzyme is a monomer with mol wt of 49.7 kD. The optimum pH and the main catalytic constants (K_M, V_max, k_cat) were determined for oxidation of the main substrates including Н₂О₂, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonate) (ABTS), 2,7-diaminofluorene, syringaldazine, 2,6-dimethoxyphenol, and o-dianisidine. The K_M values increased in the sequence: H₂O₂ < 2,7-diaminofluorene < ABTS < o-dianisidine, whereas the maximum turnover number (93.9 s^–1) was found for 2,7-diaminofluorene. Based on the analysis of molecular and catalytic properties of the enzyme, it was proven that PO-2 is a typical cationic plant peroxidase. Polycyclic aromatic hydrocarbons (phenanthrene, anthracene, fluorene), 2,2'-diphenic acid, and Ni ions had no significant influence on the activity of PO-2. The enzyme was inhibited by p-aminobenzoic acid, NaN₃, 1-naphthol, 9,10-anthraquinone, and 9,10-phenanthrenequinone. In the presence of NaN₃, 1-naphthol, and 9,10-phenanthrenequinone, a mixed competitive/noncompetitive type of inhibition was noted. The peroxidase PO-2 was found to oxidize synthetic anthraquinone dyes, phenanthrene, and some oxygenated derivatives of polycyclic aromatic hydrocarbons (9-phenanthrol; 1-naphthol; and 1-hydroxy-2-naphthoic, salicylic, and 2,2'-diphenic acids), which indirectly confirms the coupled plant–microbial metabolism of these compounds in the root zone of sorghum. The results indicate that 9,10-phenanthrenequinone and 2,2'-diphenic acid are the products of peroxidase-catalyzed oxidation of 9-phenanthrol.     

Superoxide involvement in the reduction of disulfide bonds of wheat gel proteins

A soluble epoxide hydrase which catalyzes the hydration of 9,10-epoxypalmitic acid has been partially purified from cell-free preparations from $\text{Bacillus}\text{megaterium}$ ATCC 14581. The hydrase can be cleanly separated from a soluble cytochrome P-450-dependent monooxygenase complex, previously demonstrated in this bacterium, that can catalyze the epoxidation of palmitoleic acid.     

Biosynthesis of tylosin: Oxidations of 5-O-mycaminosylprtylonolide at C-20 and C-23 with a cell-free extract from Streptomycesfradiae

The enzymatic conversion of various tylosin precursors was carried out using a cell-free system of the tylosin producer $\text{Streptomyces}\text{fradiae}$ to determine the order and intermediates of oxidations of the 16-membered branched lactone ring at C-20 and C-23 in the biosynthesis of tylosin. It was found that the order of the oxidation of the lactone is: (1) hydroxylation of 5-$\text{O}$-mycaminosylprotylonolide at C-20, (2) oxidation of C-20 hydroxymethyl to formyl, (3) hydroxylation at C-23 to give 5-$\text{O}$-mycaminosyltylonolide. The formation of 23-hydroxy-5-$\text{O}$-mycaminosylprotylonolide from 5-$\text{O}$-mycaminosylprotylonolide was not observed.     

Reactivity of chemically generated superoxide radical anion with peroxides as determined by competition kinetics

A steady-state competition system has been developed to investigate the reactions of the superoxide radical anion ($\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$) with various peroxides, including the so-called Haber-Weiss reaction. Potassium superoxide dissolved in an oxygen-free solution of DMSO containing 18-dicyclohexyl-6-crown, is the source of $\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$. High pressure liquid chromatography is used as an assay system for $\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$ reactivity, to detect and quantitate the yield of anthracene, formed as a major product in the reaction between $\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$ and 9,10-dihydroanthrancene. Decrease in anthracene yields, in the presence of peroxide, may be used to indicate a possible competing reaction between $\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$ and added peroxide. Complications involving peroxide-stimulated formation of anthraquinone derivatives are discussed. No evidence for a competing reaction between $\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$ and peroxide can be detected up to a 10-fold excess of peroxide over 9,10-dihydroanthracene.     

Isolation and preliminary characterization of 1-O-Octadec-cis-11-enyl glycerol from Paramecium phospholipids

1-O-Octadec-$\text{cis}$-11-enyl glycerol, paramecyl alcohol, was isolated from $\text{Paramecium}\text{tetraurelia}$ and $\text{P.}\text{caudatum}$ phospholipids. This isomer of 1-O-octadec-9-enyl glycerol, selachyl alcohol, had not been previously reported as a component of naturally-occurring phospholipids. The preliminary characterization of the structure of this compound was determined by 1) gas chromatography of the parent compound as well as the products following hydrogenation, ozonolysis and oxidation, 2) mass spectrometry of the parent compound and an oxidation product, 3) infrared spectroscopy, and 4) proton magnetic resonance.     

Concerning the specificity of heme oxygenase: the enzymatic oxidation of synthetic hemins.

Hemin XIII $\text{4}\text{～}$, hemin III $\text{5}\text{～}$, and iron $\text{1,4-di(β-hydroxyethyl)porphyrin}\text{6}\text{～}$ were enzymatically oxidized by a microsomal heme oxygenase preparation from rat liver. These are all better substrates of the oxygenase than the natural substrate, hemin IX $\text{1}\text{～}$. The enzymatic oxidation was selective for the α-methine bridge and in every case only the α-biliverdins were obtained. The latter were readily reduced by biliverdin reductase to the corresponding α-bilirubins. The absence of isomers in addition to the α-bilirubins was established by preparing the derived azopigments and by using [α-¹⁴C]$\text{6}\text{～}$ and [α-¹⁴C]$\text{4}\text{～}$ as substrates. The chemical oxidation of $\text{4}\text{～}$, $\text{5}\text{～}$, and $\text{6}\text{～}$ gave the expected mixture of biliverdins. It is concluded that heme oxygenase is not specific for hemin IX. On the other hand, the enzyme is highly selective for the α-methine bridge, defined as the methine opposed to that flanked by the 6,7-propionic acid residues.