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D R Boyd

Publications and source records attributed to D R Boyd.

At least 19 recordsLinked to original sources
PubMed2002

Aerobic metabolism of 4-hydroxybenzoic acid in Archaea via an unusual pathway involving an intramolecular migration (NIH shift).

A novel haloarchaeal strain, Haloarcula sp. strain D1, grew aerobically on 4-hydroxybenzoic acid (4HBA) as a sole carbon and energy source and is the first member of the domain Archaea reported to do so. Unusually, D1 metabolized 4HBA via gentisic acid rather than via protocatechuic acid, hydroquinone, or catechol. Gentisate was detected in 4HBA-grown cultures, and gentisate 1,2-dioxygenase activity was induced in 4HBA-grown cells. Stoichiometric accumulation of gentisate from 4HBA was demonstrated in 4HBA-grown cell suspensions containing 2,2'-dipyridyl (which strongly inhibits gentisate 1,2-dioxygenase). To establish whether initial 1-hydroxylation of 4HBA with concomitant 1,2-carboxyl group migration to yield gentisate occurred, 2,6-dideutero-4HBA was synthesized and used as a substrate. Deuterated gentisate was recovered from cell suspensions and identified as 3-deutero-gentisate, using gas chromatography-mass spectrometry and proton nuclear magnetic resonance spectroscopy. This structural isomer would be expected only if a 1,2-carboxyl group migration had taken place, and it provides compelling evidence that the 4HBA pathway in Haloarcula sp. strain D1 involves a hydroxylation-induced intramolecular migration. To our knowledge, this is the first report of a pathway which involves such a transformation (called an NIH shift) in the domain Archaea.

2,2'-Dipyridyl↗
PubMed2001

Aromatic dioxygenases: molecular biocatalysis and applications.

Aromatic dioxygenases have been found to catalyse single and tandem oxidation reactions of conjugated polyenes. Rational selection and design of dioxygenases, allied to substrate shape, size and substitution pattern, has been used to control regiochemistry and stereochemistry during the oxygenation process. The resulting enantiopure bioproducts have been increasingly utilised as precursors for new and alternative routes in chiral synthesis.

Bacterial Proteins↗
PubMed2000

Regioselectivity and enantioselectivity of naphthalene dioxygenase during arene cis-dihydroxylation: control by phenylalanine 352 in the alpha subunit.

The naphthalene dioxygenase (NDO) system catalyzes the first step in the degradation of naphthalene by Pseudomonas sp. strain NCIB 9816-4. The enzyme has a broad substrate range and catalyzes several types of reactions including cis-dihydroxylation, monooxygenation, and desaturation. Substitution of valine or leucine at Phe-352 near the active site iron in the alpha subunit of NDO altered the stereochemistry of naphthalene cis-dihydrodiol formed from naphthalene and also changed the region of oxidation of biphenyl and phenanthrene. In this study, we replaced Phe-352 with glycine, alanine, isoleucine, threonine, tryptophan, and tyrosine and determined the activity with naphthalene, biphenyl, and phenanthrene as substrates. NDO variants F352W and F352Y were marginally active with all substrates tested. F352G and F352A had reduced but significant activity, and F352I, F352T, F352V, and F352L had nearly wild-type activities with respect to naphthalene oxidation. All active enzymes had altered regioselectivity with biphenyl and phenanthrene. In addition, the F352V and F352T variants formed the opposite enantiomer of biphenyl cis-3,4-dihydrodiol [77 and 60% (-)-(3S,4R), respectively] to that formed by wild-type NDO [>98% (+)-(3R,4S)]. The F352V mutant enzyme also formed the opposite enantiomer of phenanthrene cis-1,2-dihydrodiol from phenanthrene to that formed by biphenyl dioxygenase from Sphingomonas yanoikuyae B8/36. A recombinant Escherichia coli strain expressing the F352V variant of NDO and the enantioselective toluene cis-dihydrodiol dehydrogenase from Pseudomonas putida F1 was used to produce enantiomerically pure (-)-biphenyl cis-(3S,4R)-dihydrodiol and (-)-phenanthrene cis-(1S,2R)-dihydrodiol from biphenyl and phenanthrene, respectively.

Anthracenes↗
PubMed1999

Contrasting effects of a nonionic surfactant on the biotransformation of polycyclic aromatic hydrocarbons to cis-dihydrodiols by soil bacteria.

The biotransformation of the polycyclic aromatic hydrocarbons (PAHs) naphthalene and phenanthrene was investigated by using two dioxygenase-expressing bacteria, Pseudomonas sp. strain 9816/11 and Sphingomonas yanoikuyae B8/36, under conditions which facilitate mass-transfer limited substrate oxidation. Both of these strains are mutants that accumulate cis-dihydrodiol metabolites under the reaction conditions used. The effects of the nonpolar solvent 2,2,4, 4,6,8,8-heptamethylnonane (HMN) and the nonionic surfactant Triton X-100 on the rate of accumulation of these metabolites were determined. HMN increased the rate of accumulation of metabolites for both microorganisms, with both substrates. The enhancement effect was most noticeable with phenanthrene, which has a lower aqueous solubility than naphthalene. Triton X-100 increased the rate of oxidation of the PAHs with strain 9816/11 with the effect being most noticeable when phenanthrene was used as a substrate. However, the surfactant inhibited the biotransformation of both naphthalene and phenanthrene with strain B8/36 under the same conditions. The observation that a nonionic surfactant could have such contrasting effects on PAH oxidation by different bacteria, which are known to be important for the degradation of these compounds in the environment, may explain why previous research on the application of the surfactants to PAH bioremediation has yielded inconclusive results. The surfactant inhibited growth of the wild-type strain S. yanoikuyae B1 on aromatic compounds but did not inhibit B8/36 dioxygenase enzyme activity in vitro.

Biodegradation, Environmental↗
PubMed1994

Chemical and enzyme-catalysed synthesis of quinoline arene hydrates.

Arene hydrates of quinoline have been synthesized by enzyme-catalysed benzylic and allylic hydroxylation of dihydroquinolines in growing cultures of the fungus Mortierella isabellina and in liver microsomal preparations. A preference for allylic hydroxylation was generally observed in eukaryotic systems. Evidence of epoxidation of dihydroarenes by both the fungal and animal enzyme systems was also obtained. The chemical synthesis of these arene hydrates (5-hydroxy-5,6-dihydroquinoline, 6-hydroxy-5,6-dihydroquinoline, 7-hydroxy-7,8-dihydroxyquinoline, and 8-hydroxy-7,8-dihydroquinoline) from the corresponding hydroxy-5,6,7,8-tetrahydroquinolines, has also been accomplished.

Animals↗
PubMed1992

Comparison of the mutagenicity of quinoline and all monohydroxyquinolines with a series of arene oxide, trans-dihydrodiol, diol epoxide, N-oxide and arene hydrate derivatives of quinoline in the Ames/Salmonella microsome test.

Fourteen new quinoline derivatives were synthesised and their mutagenicity compared in the Ames test using Salmonella typhimurium TA100 as indicator strain with and without (Aroclor-induced) S9 mix. None of the synthesised quinoline derivatives had to our knowledge been examined before in the Ames test. Quinoline and the monohydroxyquinolines were included as reference compounds. Three of the new derivatives, i.e., quinoline 7,8-oxide, N-methyl-quinoline 5,6-oxide and trans-quinoline-5,6,7,8-dioxide appeared to be mutagenic. Quinoline 7,8-oxide was positive only in the presence of S9 mix, the specific mutagenicity amounting to 2498 +/- 96 and 1289 +/- 120 revertants per mumole with 20 and 10% S9 in the mix, respectively. Both N-methyl-quinoline 5,6-oxide and trans-quinoline-5,6,7,8-dioxide were weakly positive, the former only in the presence of the S9 mix, and the latter irrespective of the presence of S9 mix, the specific mutagenicity amounting to 134 +/- 6 and 123 +/- 10 revertants per mumole, respectively. The mutagenic potency of quinoline 7,8-oxide was of the same order as that of quinoline itself and was distinctly lower than that of 8-hydroxyquinoline. Inconclusive results were obtained with trans-7,8-dihydroxy-7,8-dihydroquinoline, 5,6-dihydroxy-7,8-epoxy-5,6,7,8-tetrahydroquinoline and 8-hydroxyquinoline-N-oxide; if these compounds are mutagenic their mutagenic potency would be at least 20-30 times lower than that of the parent compounds. None of the other chemically synthesised quinoline derivatives showed mutagenic activity with TA100 either in the presence or in the absence of S9 mix. The results obtained with the reference compounds were in accordance with literature data.

Animals↗
PubMed1990

Preferential modification of guanine bases in DNA by dimethyldioxirane and its application to DNA sequencing.

From gel sequencing experiments with 32P-end-labelled oligodeoxyribonucleotides, it is shown that treatment of DNA with the powerful oxidant dimethyldioxirane, followed by heating in piperidine, causes selective strand scission at the sites of guanine bases. The same specificity for cleavage at guanine was observed with a 45-mer labelled at either the 3'- or 5'-end and with a single and double stranded 34-mer. On account of its speed and operational simplicity, modification with dimethyldioxirane is proposed as a practicable alternative to conventional chemical sequencing procedures for locating guanine bases in DNA.

Base Sequence↗
PubMed1987

Stereoselective formation of benzo(c)phenanthrene (+)-(3S,4R) and (+)-(5S,6R)-oxides by cytochrome P450c in a highly purified and reconstituted system.

The principal oxidative metabolites formed from benzo(c)phenanthrene (B(c)Ph) by the cytochromes P450 in liver microsomes from control and treated rats are the 3,4- and 5,6-arene oxides. A procedure is described which allows determination of the enantiomer composition and absolute configuration of these arene oxides based on HPLC separation of isomeric thiolate adducts formed with N-acetyl-L-cysteine in base. Incubation of [3H]-B(c)Ph with highly purified cytochrome P450c in a reconstituted monooxygenase system followed by trapping of the metabolically formed arene oxides as above indicated that the 3,4-oxide was predominantly the (+)-(3S,4R)-enantiomer (90%) and that the 5,6-oxide consisted mainly of the (+)-(5S,6R)-enantiomer (76%). The results are discussed in terms of their implications about the catalytic binding site of cytochrome P450c.

Animals↗
PubMed1982

Epidemiology of minor burn injuries.

The incidence of minor burn injuries has been determined for the Commonwealth of Virginia during a 17-month period. The data set included all patients with burn injuries receiving treatment in the emergency department that did not require hospitalization. The risk of burn injury was calculated by age, race and sex. Examination of the data revealed large differences in the magnitude of age-specific incidence rates between men and women and the white and non-white population. Differences in the economic status of the population may explain a large proportion of the variation in the crude burn rates.

Adolescent↗
PubMed1980

An enantiomeric interaction in the metabolism and tumorigenicity of (+)- and (-)-benzo[a]pyrene 7,8-oxide.

The (+)- and (-)-enantiomers of benzo[a]pyrene 7,8-oxide are hydrated stereospecifically at C-8 to (-)- and (+)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene, respectively, by rat hepatic epoxide hydrolase. The (-)-enantiomer of benzo[a]pyrene 7,8-oxide is metabolized by microsomal epoxide hydrolase at a rate 3- to 4-fold greater than the (+)-enantiomer. At low conversion of racemic substrate, however, benzo[a]pyrene 7,8-oxide is metabolized to the dihydrodiol at a rate equal to that of the (+)-enantiomer. An analysis of the enantiomeric composition of the dihydrodiol formed from the racemic substrate revealed preferential formation of (-)-trans-7,8-dihydroxy-7,8-dihydrobenzo-[a]pyrene. At low substrate conversion (< 20% metabolism), the enantiomeric purity of the dihydrodiol was much higher than at high substrate conversion (> 50% metabolism). Similar results were obtained with microsomes from hamster, rabbit, guinea pig, mouse, and human liver. These results indicate that epoxide hydrolase has a higher affinity for (+)-benzo[a]pyrene 7,8-oxide than for the (-)-enantiomer. The kinetics of hydration of (+)- and (-)-benzo[a]pyrene 7,8-oxide by purified epoxide hydrolase in detergent solution showed the (+)- and (-)-enantiomers to have apparent Km values of 1.7 and greater than or equal to 20 microM, respectively. Tumorigenicity studies with benzo[a]pyrene 7,8-oxide on mouse skin and in newborn mice revealed that (+)-benzo[a]pyrene 7,8-oxide, the metabolic precursor of the more tumorigenic (-)-7,8-dihydrodiol, is significantly more tumorigenic than the (-)-enantiomer. However, racemic benzo[a]pyrene 7,8-oxide was more tumorigenic than either enantiomer alone, indicating an enantiomeric synergism in the carcinogenicity of benzo[a]pyrene 7,8-oxide. The data are discussed in relation to the complete sequence of metabolic pathways leading to an ultimate carcinogen from benzo[a]pyrene.

Animals↗
PubMed1980

The role of the Emergency Medical Services in organ donation.

A potential need for more organ donors has been identified because of the improved survival rates of patients receiving kidney transplants and the reports of improving graft success rates. Because of the development of the EMS trauma program, an awareness of the potential benefit for increased organ donation could be realized by improved working relationship of the EMS trauma unit and the organ recovery agency. In the final analysis, careful planning of a regionwide program for organ recovery by the organ retrieval groups to include the EMS trauma unit should result in an increased number of cadaveric kidneys for transplantation.

Cadaver↗