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J R Lloyd

Publications and source records attributed to J R Lloyd.

At least 37 records · Page 2Linked to original sources
PubMed1999

Reduction of technetium by Desulfovibrio desulfuricans: biocatalyst characterization and use in a flowthrough bioreactor.

Resting cells of Desulfovibrio desulfuricans coupled the oxidation of a range of electron donors to Tc(VII) reduction. The reduced technetium was precipitated as an insoluble low-valence oxide. The optimum electron donor for the biotransformation was hydrogen, although rapid rates of reduction were also supported when formate or pyruvate was supplied to the cells. Technetium reduction was less efficient when the growth substrates lactate and ethanol were supplied as electron donors, while glycerol, succinate, acetate, and methanol supported negligible reduction. Enzyme activity was stable for several weeks and was insensitive to oxygen. Transmission electron microscopy showed that the radionuclide was precipitated at the periphery of the cell. Cells poisoned with Cu(II), which is selective for periplasmic but not cytoplasmic hydrogenases, were unable to reduce Tc(VII), a result consistent with the involvement of a periplasmic hydrogenase in Tc(VII) reduction. Resting cells, immobilized in a flowthrough membrane bioreactor and supplied with Tc(VII)-supplemented solution, accumulated substantial quantities of the radionuclide when formate was supplied as the electron donor, indicating the potential of this organism as a biocatalyst to treat Tc-contaminated wastewaters.

Biodegradation, Environmental↗
PubMed1999

The periplasmic 9.6-kilodalton c-type cytochrome of Geobacter sulfurreducens is not an electron shuttle to Fe(III).

Geobacter sulfurreducens contains a 9.6-kDa c-type cytochrome that was previously proposed to serve as an extracellular electron shuttle to insoluble Fe(III) oxides. However, when the cytochrome was added to washed-cell suspensions of G. sulfurreducens it did not enhance Fe(III) oxide reduction, whereas similar concentrations of the known electron shuttle, anthraquinone-2,6-disulfonate, greatly stimulated Fe(III) oxide reduction. Furthermore, analysis of the extracellular c-type cytochromes in cultures of G. sulfurreducens demonstrated that the dominant c-type cytochrome was not the 9.6-kDa cytochrome, but rather a 41-kDa cytochrome. These results and other considerations suggest that the 9.6-kDa cytochrome is not an important extracellular electron shuttle to Fe(III) oxides.

Cytochrome c Group↗
PubMed1999

Microbial reduction of technetium by Escherichia coli and Desulfovibrio desulfuricans: enhancement via the use of high-activity strains and effect of process parameters.

Escherichia coli and Desulfovibrio desulfuricans reduce Tc(VII) (TcO(4)(-)) with formate or hydrogen as electron donors. The reaction is catalyzed by the hydrogenase component of the formate hydrogenlyase complex (FHL) of E. coli and is associated with a periplasmic hydrogenase activity in D. desulfuricans. Tc(VII) reduction in E. coli by H(2) and formate was either inhibited or repressed by 10 mM nitrate. By contrast, Tc(VII) reduction catalyzed by D. desulfuricans was less sensitive to nitrate when formate was the electron donor, and unaffected by 10 mM or 100 mM nitrate when H(2) was the electron donor. The optimum pH for Tc(VII) reduction by both organisms was 5.5 and the optimum temperature was 40 degrees C and 20 degrees C for E. coli and D. desulfuricans, respectively. Both strains had an apparent K(m) for Tc(VII) of 0.5 mM, but Tc(VII) was removed from a solution of 300 nM TcO(4)(-) within 30 h by D. desulfuricans at the expense of H(2). The greater bioprocess potential of D. desulfuricans was shown also by the K(s) for formate (>25 mM and 0.5 mM for E. coli and D. desulfuricans, respectively), attributable to the more accessible, periplasmic localization of the enzyme in the latter. The relative rates of Tc(VII) reduction for E. coli and D. desulfuricans (with H(2)) were 12.5 and 800 micromol Tc(VII) reduced/g biomass/h, but the use of an E. coli HycA mutant (which upregulates FHL activities by approx. 50%) had a similarly enhancing effect on the rate of Tc reduction. The more rapid reduction of Tc(VII) by D. desulfuricans compared with the E. coli strains was also shown using cells immobilized in a hollow-fiber reactor, in which the flow residence times sustaining steady-state removal of 80% of the radionuclide were 24.3 h for the wild-type E. coli, 4.25 h for the upregulated mutant, and 1.5 h for D. desulfuricans.

Biomass↗
PubMed1998

Detection of heavy metal ions at femtomolar levels using protein-based biosensors.

Sensors based on proteins (GST-SmtA and MerR) with distinct binding sites for heavy metal ions were developed and characterized. A capacitive signal transducer was used to measure the conformational change following binding. The proteins were overexpressed in Escherichia coli, purified, and immobilized in different ways to a self-assembled thiol layer on a gold electrode placed as the working electrode in a potentiostatic arrangement in a flow analysis system. The selectivity and the sensitivity of the two protein-based biosensors were measured and compared for copper, cadmium, mercury, and zinc ions. The GST-SmtA electrodes displayed a broader selectivity (sensing all four heavy metal ions) compared with the MerR-based ones, which showed an accentuated selectivity for mercury ions. Metal ions could be detected with both electrode types down to femtomolar concentration. The upper measuring limits, presumably due to near saturation of the proteins' binding sites, were around 10(-10) M. Control electrodes similarly constructed but based on bovine serum albumin or urease did not yield any signals. The electrodes could be regenerated with EDTA and used for more than 2 weeks with about 40% reduction in sensitivity.

Amino Acid Sequence↗
PubMed1998

Mutations in the gene encoding starch synthase II profoundly alter amylopectin structure in pea embryos.

Mutations at the rug5 (rugosus5) locus have been used to elucidate the role of the major soluble isoform of starch synthase II (SSII) in amylopectin synthesis in the developing pea embryo. The SSII gene maps to the rug5 locus, and the gene in one of three rug5 mutant lines has been shown to carry a base pair substitution that introduces a stop codon into the open reading frame. All three mutant alleles cause a dramatic reduction or loss of the SSII protein. The mutations have pleiotropic effects on the activities of other isoforms of starch synthase but apparently not on those of other enzymes of starch synthesis. These mutations result in abnormal starch granule morphology and amylopectin structure. Amylopectin contains fewer chains of intermediate length (B2 and B3 chains) and more very short and very long chains than does amylopectin from wild-type embryos. The results suggest that SSII may play a specific role in the synthesis of B2 and B3 chains of amylopectin. The extent to which these findings can be extrapolated to other species is discussed.

Amylopectin↗
PubMed1997

Immobilisation of whole bacterial cells for anaerobic biotransformations.

Anaerobically grown cells of Escherichia coli were immobilised within a range of entrapment matrices and packed into a column under standard conditions, and the ability of the immobilised cells to reduce nitrite (0.5 mM) was measured at a range of flow rates using sodium formate (20 mM) as the electron donor for nitrite reduction. A flow-rate/activity plot was constructed for each flow-through reactor and RA1/2 values (residence time corresponding to 50% nitrite removal) calculated for each reactor type. Cells immobilised in flat and hollow-fibre membranes were the most effective (RA1/2 = 0.35 h and 0.47 h respectively), with cells entrapped by dialysis membrane (1.53 h), alginate beads (1.93 h), Hypol foam (2.31 h) and polyacrylamide gel (50% nitrite not removed at maximum residence time tested: 4.9 h) performing progressively less effectively. Cells grown as a biofilm on a range of support materials were also tested in comparable packed-bed reactors. Cell loss from these supports was extensive and contributed to poor performance of the reactors despite high initial biomass loadings (RA1/2 values using raschig rings, coke and activated-carbon supports: 1.6 h, 2.3 h and 1.0 h respectively). Biofilms grown on Pharmacia microcarrier supports and used in packed and also fluidised beds were more stable and the performance of these reactors was superior to that of biofilm reactors using other supports, and comparable to that of the membrane reactors (RA1/2 values for Cytoline 2, Cytopore 2 and Cytodex 3: 0.76 h, 0.56 h, 0.68 h respectively).

Acrylic Resins↗
PubMed1997

Hollow-fire bioreactors compared to batch and chemostat culture for the production of a recombinant toxoid by a marine Iibrio.

Bioreactor selection is important for maximising the productivity of recombinant organisms. In this paper a comparison is made between growth and recombinant protein synthesis in three types of bioreactor containing a marine Vibrio capable of heterologous expression and secretion of the non-toxic B-subunit pentamer of Escherichia coli heat-labile enterotoxin, EtxB. The heterologous gene was located on the plasmid pMMB68. Resistance to carbenicillin was used to select for plasmid-containing cells. In batch and continuous culture. Volumetric productivities were highest when cells were grown in the presence of carbenicillin. Without antibiotic selection, the highest volumetric productivity (9.4 mg EtxB-1 h-1) was observed in hollow-fibre bioreactors, and the production phase could be maintained for over 50 h. The highest specific productivity under these conditions was found in batch culture, but the maximal production phase was only of 5 h duration. In hollow-fibre reactors the type of fibre used significantly affected productivity, both with regards to the maintenance of reactor integrity and by allowing passage of the recombinant toxoid through the selectively permeable membrane. Where contamination of the product with carbenicillin is to be avoided, these bioreactors are superior to batch or continuous culture.

Bacterial Toxins↗
PubMed1997

Reduction and removal of heptavalent technetium from solution by Escherichia coli.

Anaerobic, but not aerobic, cultures of Escherichia coli accumulated Tc(VII) and reduced it to a black insoluble precipitate. Tc was the predominant element detected when the precipitate was analyzed by proton-induced X-ray emission. Electron microscopy in combination with energy-dispersive X-ray analysis showed that the site of Tc deposition was intracellular. It is proposed that Tc precipitation was a result of enzymatically mediated reduction of Tc(VII) to an insoluble oxide. Formate was an effective electron donor for Tc(VII) reduction which could be replaced by pyruvate, glucose, or glycerol but not by acetate, lactate, succinate, or ethanol. Mutants defective in the synthesis of the transcription factor FNR, in molybdenum cofactor (molybdopterin guanine dinucleotide [MGD]) synthesis, or in formate dehydrogenase H synthesis were all defective in Tc(VII) reduction, implicating a role for the formate hydrogenlyase complex in Tc(VII) reduction. The following observations confirmed that the hydrogenase III (Hyc) component of formate hydrogenlyase in both essential and sufficient for Tc(VII) reduction: (i) dihydrogen could replace formate as an effective electron donor for Tc(VII) reduction by wild-type bacteria and mutants defective in MGD synthesis; (ii) the inability of fnr mutants to reduce Tc(VII) can be suppressed phenotypically by growth with 250 microM Ni2+ and formate; (iii) Tc(VII) reduction is defective in a hyc mutant; (iv) the ability to reduce Tc(VII) was repressed during anaerobic growth in the presence of nitrate, but this repression was counteracted by the addition of formate to the growth medium; (v) H2, but not formate, was an effective electron donor for a Sel- mutant which is unable to incorporate selenocysteine into any of the three known formate dehydrogenases of E. coli. This appears to be the first report of Hyc functioning as an H2-oxidizing hydrogenase or as a dissimilatory metal ion reductase in enteric bacteria.

Anaerobiosis↗
PubMed1996

School daze.

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Biology↗
PubMed1996

A Novel PhosphorImager-Based Technique for Monitoring the Microbial Reduction of Technetium.

A novel PhosphorImager-based technique which can be used to quantify low concentrations of radionuclides is described. The technique offers several benefits, combining very high sensitivity with containment of the radioisotope in the solid state, thus minimizing disposal procedures. In this study, it was used in conjunction with paper chromatography to quantify different oxidation states of (sup99)Tc in solution. The technique was used to evaluate the potential of anaerobic cultures of Shewanella putrefaciens and Geobacter metallireducens (bacteria with known metal-reducing capabilities) to reduce highly soluble Tc(VII) to insoluble lower-valence species, facilitating its removal from solution. Both organisms reduced Tc(VII), but profiles of Tc species produced in culture supernatants were strain specific. S. putrefaciens produced Tc(V), Tc(IV), and one unidentified species, but no Tc was removed from solution. G. metallireducens removed 70% of the 250 (mu)M Tc added in solution, with trace amounts of Tc(V) and the unidentified species detected in culture supernatants. Possible uses for these organisms in the bioremediation of Tc-contaminated waters are discussed, and other uses of the PhosphorImager technique are highlighted.

Journal Article↗
PubMed1992

Radiofrequency energy for rewarming of cold extremities.

Radiofrequency (RF) coils, developed to resonate at 27.12 MHz, were evaluated for effectiveness in rewarming thermally unprotected extremities of 5 male subjects. Bare hands or bare feet were exposed to 10.0 degrees C air during a total of four exposures for each subject. Deposition of RF energy for two of the exposures (one for the hands and one for the feet) began when a predetermined surface skin temperature was achieved. Rewarming continued for 10 min while fiber-optic sensors recorded surface skin temperatures at eight locations for each hand and four locations for each foot. Results were compared to data from identical exposures but without RF rewarming. Statistically significant (P less than 0.01) warming occurred at all of the monitored locations. Our results clearly demonstrate the ability of RF energy to warm hands and feet in cold environments.

Adult↗
PubMed1991

Characterization of the solution degradation products of histrelin, a gonadotropin releasing hormone (LH/RH) agonist.

The degradation products of histrelin (1, less than Glu-His-Trp-Ser-Tyr-(D-Nim-bzl-His)-Leu-Arg-Pro-NHEt) were determined in aqueous solution at pH 5.4 and 87 degrees C over an 18-day period (47% degradation). These degradation products (2-5) resulted from the cleavage of less than Glu-His and Trp-Ser peptide bonds, His-Trp diketopiperazine formation, and racemization of serine and histidine residues.

Amino Acid Sequence↗
PubMed1991

All-trans retinoic acid protects against conversion of chemically induced and ultraviolet B radiation-induced skin papillomas to carcinomas.

It is becoming increasingly clear that cutaneous carcinogenesis in murine skin is a stepwise process comprising of initiation, promotion and progression. Most of the papillomas induced by an initiation-promotion protocol regress, while a few of them progress to malignant carcinomas. Progression of benign tumors into malignant cancer is critical since the latter lesions are capable of metastatic spread and eventual death. Inhibitors of the conversion process are therefore likely to be useful as cancer chemopreventive agents. All-trans retinoic acid (RA) is a known regulator of cellular proliferation and differentiation, and a known inhibitor of tumor promotion in murine skin. In this study we assessed the effect of topical application of RA on conversion of benign skin papillomas to malignant carcinomas. Papillomas were induced in SENCAR mice by topical application of 7,12-dimethylbenz[a]anthracene (DMBA) as tumor initiator followed by 12-O-tetradecanoylphorbol-13-acetate (TPA) as tumor promoter. In SKH-1 hairless mice papillomas were induced by thrice weekly exposure to ultraviolet B (UVB) radiation. At 18 (DMBA/TPA group) and 25 (UVB group) weeks papilloma yield stabilized and no new tumors developed. Beginning at the 20th week (DMBA/TPA group) and at the 27th week (UVB group), malignant conversion was achieved by twice weekly topical application of TPA or free radical-generating compounds benzoyl peroxide (BPO), 2,2-azobis(2-amidinopropane) (ABP) and tert-butyl peroxybenzoate (BPB). Application of RA (10 micrograms/animal) 1 h prior to skin application of TPA, BPO, ABP or BPB afforded significant protection (up to 70%) only against malignant conversion mediated by free radical-generating compounds in both chemically induced and UVB-induced benign skin papillomas. On the other hand, preapplication of RA was less effective in the suppression of spontaneous malignant conversion in vehicle-treated animals. These results suggest that, in addition to their anti-tumor promoting effects, retinoids may also act as anti-carcinogens by inhibiting the process of malignant conversion induced by free radical-generating compounds.

Animals↗
PubMed1989

Characterization of the solution degradation products of etintidine, an H2-receptor antagonist.

The primary solution degradation products of the antiulcer drug etintidine (1, N"-cyano-N-[2-[[(5-methyl-1H-imidazol-4-yl)methyl]thio]ethyl]- N'-2-propynylguanidine) were determined to be the guanyl urea 2, the guanidine 3, the amine 4a, and the cyanoamine 4b. These products resulted from nitrile hydrolysis and/or intramolecular cyclization of the guanidino and propargyl groups. The amine 4a was found to be a predominant degradation product in aqueous media of pH 4-7 at 70 +/- 0.2 degrees C.

Chromatography, High Pressure Liquid↗
PubMed1989

Malignant conversion of UV radiation and chemically induced mouse skin benign tumors by free-radical-generating compounds.

It is known that the free-radical-generating compound, benzoyl peroxide (BPO) enhances malignant conversion of murine skin benign papillomas into carcinomas. To further define the role of free radicals in malignant conversion, we studied the effect of various free-radical-generating compounds on the conversion of benign papillomas into carcinomas in murine skin. Papillomas were induced in Sencar mice by 7,12-dimethylbenz[a]anthracene (DMBA) initiation and 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion and in SKH-1 hairless mice by biweekly exposure to UVB radiation. After 20 and 27 weeks respectively, papilloma yield stabilized and no new tumors developed. Skin application of acetone, TPA, BPO, 2,2-azobis(2-amidino-propane) (ABP) and tert-butyl hydroperoxybenzoic acid (BPB) increased the rate of malignant conversion in both Sencar and SKH-1 mice. In general, the rate of malignant conversion was faster in UVB-induced tumors compared with DMBA-induced tumors. The relative efficacy of each agent was similar in both groups and was in the order: acetone less than TPA less than BPB less than BPO less than ABP. Our data suggest that free-radical-generating compounds may accelerate the malignant conversion of benign papillomas into carcinoma, indicating that epigenetic mechanism(s) may also be involved in this process.

9,10-Dimethyl-1,2-benzanthracene↗