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Biomedical subjects

D T Gibson

Publications and source records attributed to D T Gibson.

At least 109 records · Page 6Linked to original sources
PubMed1979

Bacterial and fungal oxidation of dibenzofuran.

Cunninghamella elegans and a mutant strain (B8/36) of Beijerinckia both oxidized dibenzofuran to 2,3-dihydroxy-2,3-dihydrodibenzofuran. The bacterial metabolite was extremely unstable and, in the presence of acid, was rapidly converted into a mixture of 2- and 3-hydroxydibenzofuran. In contrast, the 2,3-dihydroxy-2,3-dihydrodibenzofuran formed by C. elegans was stable and only yielded 2- and 3-hydroxydibenzofuran when heated under acidic conditions. The results suggest that Beijerinckia B8/36 and C. elegans form the respective cis- and trans-isomers of 2,3-dihydroxy-2,3-dihydrodibenzofuran. C. elegans also oxidized dibenzofuran to 2- and 3-hydroxydibenzofuran under conditions that would not lead to the dehydration of the trans-dihydrodiol. These observations implicate the initial formation of dibenzofuran- 2,3-epoxide in the fungal oxidation of dibenzofuran. Beijerinckia B8/36 also produced a second unstable dihydrodiol that was tentatively identified as cis-1,2-dihydroxy-1,2-dihydrodibenzofuran. This compound gave 2-hydroxydibenzofuran as the major dehydration product and the cis relative stereochemistry was suggested by the isolation and characterization of an isopropylidine derivative. A preparation of cis-naphthalene dihydrodiol dehydrogenase and cell extracts of the parent strain of Beijerinckia oxidized both bacterial dihydrodiols to catechols. Cell extracts prepared from C. elegans catalysed an analogous oxidation of trans-2,3-dihydroxy-2,3-dihydrodibenzofuran to 2,3-dihydroxydibenzofuran. The latter product was also isolated and identified from culture filtrates. The results suggest that bacteria and fungi utilize different mechanisms to initiate the oxidation of dibenzofuran.

Bacteria↗
PubMed1979

Fungal metabolism of biphenyl.

Cunninghamella elegans grown on Sabouraud dextrose broth transformed biphenyl to produce 2-, 3- and 4-hydroxybiphenyl, as well as 4,4'-dihydroxybiphenyl as free phenols. A compound tentatively identified as 2,4'-dihydroxybiphenyl was also produced. When 4-hydroxybiphenyl or 2-hydroxybiphenyl replaced biphenyl as the substrate, C. elegans produced 4,4'-dihydroxybiphenyl and 2,5-dihydroxybiphenyl respectively. The compound identified as 2,4'-dihydroxybiphenyl was produced from both substrates. A survey of 11 species of fungi known to degrade hydrocarbons revealed two species that were comparable to C. elegans in their ability to convert biphenyl into free phenols. In addition to free phenolic metabolites, deconjugation experiments indicated that 44% of the known metabolites present in the culture filtrate were present in the form of conjugates. These results suggest that the transformation of biphenyl by C. elegans is similar to that found in mammalian systems.

Biphenyl Compounds↗
PubMed1979

Emulsifier of Arthrobacter RAG-1: specificity of hydrocarbon substrate.

The purified extracellular emulsifying factor produced by Arthrobacter RAG-1 (EF-RAG) emulsified light petroleum oil, diesel oil, and a variety of crude oils and gas oils. Although kerosine and gasoline were emulsified poorly by EF-RAG, they were converted into good substrates for emulsification by addition of aromatic compounds, such as 2-methylnaphthalene. Neither aromatic nor aliphatic fractions of crude oil were emulsified by EF-RAG; however, mixtures containing both fractions were emulsified. Pure aliphatic or aromatic hydrocarbons were emulsified poorly by EF-RAG. Binary mixtures containing an aliphatic and an aromatic hydrocarbon, however, were excellent substrates for EF-RAG-induced emulsification. Of a variety of alkylcyclohexane and alkylbenzene derivatives tested, only hexyl- or heptylbenzene and octyl- or decylcyclohexane were effectively emulsified by EF-RAG. These data indicate that for EF-RAG to induce emulsification of hydrocarbons in water, the hydrocarbon substrate must contain both aliphatic and cyclic components. With binary mixtures of methylnaphthalene and hexadecane, maximum emulsion was obtained with 25% hexadecane.

Arthrobacter↗
PubMed1978

Fungal transformation of naphthalene.

Eighty-six species of fungi belonging to sixty-four genera were examined for their ability to metabolize naphthalene. Analysis by thin-layer and high pressure liquid chromatography revealed that naphthalene metabolism occurred in forty-seven species belonging to thirty-four genera from the major fungal taxa. All organisms tested from the order Mucorales oxidized naphthalene with species of Cunninghamella, Syncephalastrum and Mucor showing the greatest activity. Significant metabolism was also observed with Neurospora crassa, Claviceps paspali and four species of Psilocybe. The predominant metabolite formed by most organisms was 1-naphthol. Other products identified were, 4-hydroxy-1-tetralone, trans-1,2-dihydroxy-1,2-dihydronaphthalene, 2-naphthol, 1,2-and 1,4-naphthoquinone.

Chromatography, High Pressure Liquid↗
PubMed1977

Metabolism of naphthalene by Cunninghamella elegans.

Cunninghamella elegans grown on Sabouraud dextrose broth in the presence of naphthalene produced six metabolites. Each product was isolated and identified by conventional chemical techniques. The major metabolites were 1-naphthol (67.9%) and 4-hydroxy-1-tetralone (16.7%). Minor products isolated were 1,4-naphthoquinone (2.8%), 1,2-naphthoquinone (0.2%), 2-naphthol (6.3%), and trans-1,2-dihydroxy-1,2-dihydronaphthalene (5.3%). C. elegans oxidized both 1-naphthol and 1,4-naphthoquinone to 4-hydroxy-1-tetralone. The results suggest that C. elegans oxidizes naphthalene by a sequence of reactions similar to those reported for the mammalian metabolism of this hydrocarbon.

Chemical Phenomena↗
PubMed1977

Metabolism of dibenzothiophene by a Beijerinckia species.

Beijerinckia B8/36 when grown with succinate in the presence of dibenzothiophene, accumulated (+)-cis-1,2-dihydroxy-1,2-dihydrodibenzothiophene and dibenzothiophene-5-oxide in the culture medium. Each metabolite was isolated in crystalline form and characterized by a variety of chemical techniques, cis-Naphthalene dihydrodiol dehydrogenase, isolated from Pseudomonas putida, oxidized (+)-cis-1,2-dihydroxy-1,2-dihydrodibenzothiophene to a compound that was tentatively identified as 1,2-dihydroxydibenzothiophene. The same product was formed when crude cell extracts of the parent strain of Beijerinckia oxidized (+)-cis-1,2-dihydroxy-1,2-dihydrodibenzothiophene under anaerobic conditions. Further metabolism of 1,2-dihydroxydibenzothiophene by heat-treated cell extracts led to the formation of 4[2-(3-hydroxy)-thionaphthenyl]-2-oxo-3-butenoic acid. The latter compound was metabolized by crude cell extracts to 3-hydroxy-2-formylthionaphthene. Further degradation of this metabolite was not observed.

Cell-Free System↗
PubMed1977

Purification and properties of cis-toluene dihydrodiol dehydrogenase from Pseudomonas putida.

The purification of (+)-cis-1(S),2(R)-dihydroxy-3-methylcyclohexa-3,5-diene dehydrogenase from cells of Pseudomonas putida grown with toluene as the sole source of carbon and energy is reported. The molecular weight of the enzyme is 104,000 at pH 9.7. The enzyme is composed of four apparently identical subunits with molecular weights of 27,000. The enzyme is specific for nicotinamide adenine dinucleotide and oxidizes a number of cis-dihydrodiols. Both enantiomers of a racemic mixture of cis-1,2-dihydroxyl-1,2-dihydronaphthalene dihydrodiol are oxidized by the enzyme. No enzymatic activity is observed with trans-1,2-dihydroxyl-1,2-dihydronaphthalene dihydrodiol.

Amino Acids↗
PubMed1976

XYL, a nonconjugative xylene-degradative plasmid in Pseudomonas Pxy.

Pseudomanas Pxy metabolizes p- or m-xylene through intermediate formation of the corresponding methylbenzyl alcohol and toluic acid via the meta pathway. The strain Pseudomonas Pxy spontaneously loses its ability to grow with xylene or toluate, and the rate of loss of this ability is greatly enhanced by treatment of the cells with mitomycin C. The assay of enzymes involved in xylene degradation in xylene-negative Pxy cells indicates the loss of the entire enzyme complement of the pathway. The genes specifying all the xylene-degradative enzymes, including those of the meta pathway, appear to be borne on a nonconjugative plasmid and can be transferred to xylene-negative Pxy or P. putida strain PpG1 cells only in the presence of a transfer plasmid termed factor K. When transferred to strain PpG1, the xylene-degradative plasmid, termed XYL, coexists stably with factor K, but transduction of XYL is not accompanied by a cotransfer of factor K. XYL appears to be compatible wit- all the other known degradative plasmids in P. putida. The xylene pathway is inducible in wild-type Pxy as well as in Pxy and PpG1 exconjugants, suggesting the cotransfer of regulatory genes along with the plasmid. The enzymes converting xylene to toluate are induced by xylene, methylbenzyl alcohol, or the aldehyde derivatives but not significantly by toluate, whereas catechol dioxygenase and other enzymes are induced by toluates and presumable by xylene as well.

Benzyl Alcohols↗
PubMed1976

Bacterial cis-dihydrodiol dehydrogenases: comparison of physicochemical and immunological protperties.

Cells of Pseudomonas putida NP, Pseudomonas species (NCIB 9816), and a Nocardia species, after growth on naphthalene as sole source of carbon and energy, contain a nicotinamide adenine dinucleotide (NAD+)-dependent enzyme that oxidizes cis-dihydrodiols of mono- and polycyclic aromatic compounds. Similarly, cells of a strain of P. putida biotype A, when grown either on toluene or benzene vapors, were found to contain a dehydrogenase that oxidized dihydrodiols of aromatic hydrocarbons with cis stereochemistry and required NAD+ as an electron acceptor. In all these cases, no enzymatic activity was detected when trans-naphthalene dihydrodiol was used as a substrate. Purified cis-naphthalene dihydrodiol dehydrogenase was injected into rabbits to obtain antibodies. Physiocochemical and immunological properties of cis-dihydrodiol:NAD+ oxidoreductases from four different organisms were examined. Kinetic analysis showed that, in all the cases, enzymes exhibited higher affinity for cis-dihydrodiols than for NAD+ and had pH optima between 8.8 and 9.0. except in the case of the enzyme from Nocarida sp., which showed maximum activity at pH 8.4. Molecular-weight determination of the dehydrogenases from the four different organisms by gel filtration on a Sephadex G-200 column gave values ranging from 92,000 for the enzyme from Nocardia sp. to 160,000 for that from P. putida biotype A. All the dehydrogenases, except the one from Nocardia sp., exhibited immunological cross-reaction with the antibodies prepared against the enzyme purified from P. putida NP.

Alcohol Oxidoreductases↗
PubMed1976

Initial reactions in the bacterial degradation of aromatic hydrocarbons.

Bacteria incorporate two atoms of molecular oxygen into aromatic hydrocarbons with the formation of cis dihydrodiols. The production of cis dihydrodiols has been demonstrated for substrates that range in size from benzene to benzo[a]pyrene. These results are in direct contrast to the mechanisms utilized by mammals, and possibly all eucaryotic organisms, for the oxidation of aromatic hydrocarbons. Thus, mammals incorporate one atom of molecular oxygen into these substrates to form arene oxides. Hydration of the latter compounds produces dihydrodiols that have a trans stereochemistry.

Alcohol Oxidoreductases↗
PubMed1975

Oxidation of the carcinogens benzo [a] pyrene and benzo [a] anthracene to dihydrodiols by a bacterium.

A mutant strain of Beijerinckia, after growth with succinate plus biphenyl, contains an enzyme system that oxidizes benzo [a] pyrene and benzo [a] anthracene to mixtures of vicinal dihydrodiols. The major dihydrodiol formed from benzo [a] pyrene was identified as cis-9, 10-dihydroxy-9, 10-dihydrobenzo [a] pyrene by comparison with a synthetic sample. Benzo [a] anthracene was metabolized to four dihydrodiols, the major isomer being cis-1, 2-dihydroxy-1, 2-dihydroxy-1, 2-dihydrobenzo [a] anthracene.

Azotobacter↗
PubMed1975

Initial reactions in the oxidation of naphthalene by Pseudomonas putida.

A strain of Pseudomonas putida that can utilize naphthalene as its sole source of carbon and energy was isolated from soil. A mutant strain of this organism, P. putida 119, when grown on glucose in the presence of naphthalene, accumulates optically pure (+)-cis-1(R),2(S)-dihydroxy-1,2-dihydronaphthalene in the culture medium. The cis relative stereochemistry in this molecule was established by nuclear magnetic resonance spectrometry. Radiochemical trapping experiments established that this cis dihydrodiol is an intermediate in the metabolism of naphthalene by P. Fluorescens (formerly ATCC, 17483), P. putida (ATCC, 17484), and a Pseudomonas species (NCIB 9816), as well as the parent strain of P. putida described in this report. Formation of the cis dihydrodiol is catalyzed by a dioxygenase which requires either NADH or NADPH as an electron donor. A double label procedure is described for determining the origin of oxygen in the cis dihydrodiol under conditions where this metabolite would not normally accumulate. Several aromatic hydrocarbons are oxidized by cell extracts prepared from naphthalene-grown cells of P. putida. The cis dihydrodiol is converted to 1,2-dihydroxynaphthalene by an NAD+-dependent dehydrogenase. This enzyme is specific for the (+) isomer of the dihydrodiol and shows a primary isotope effect when the dihydrodiol is substituted at C-2 with deuterium.

Culture Media↗