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Biomedical subjects

D B Scott

Publications and source records attributed to D B Scott.

At least 19 recordsLinked to original sources
PubMed1992

Surrogate transformation of perennial ryegrass, Lolium perenne, using genetically modified Acremonium endophyte.

Conditions have been developed for transforming protoplasts of the perennial ryegrass endophyte Acremonium strain 187BB. Unlike most other ryegrass endophytes, this strain does not produce the lolitrem B neurotoxin and is therefore suitable as a host for surrogate introduction of foreign genes into grasses. Transformation frequencies of 700-800 transformants/micrograms DNA were obtained for both linear and circular forms of pAN7-1, a hygromycin (hph) resistant plasmid. Up to 80% of the linear transformants were stable on further culturing but only 25% of the circular transformants retained hygromycin resistance. Integration of pAN7-1 into the genome was confirmed by Southern blotting and probing of genomic digests of transformant DNA. Both single and tandemly repeated copies of the plasmid were found in the genome and both the number and sites of integration varied among the transformants. At least 13 chromosomes were identified in 187BB using contour-clamped homogeneous electric field (CHEF) gel electrophoresis. Probing of Southern blots of these gels confirmed that pAN7-1 had integrated into different chromosomes. The beta-glucuronidase (GUS) gene, uidA, was also introduced into 187BB by co-transformation of pNOM-2 with pAN7-1. GUS activity was detected by growing the transformants on plates containing 5-bromo-4-chloro-3-indolyl beta-D-glucuronic acid and by enzyme assays of mycelial extracts. Several hph- and uidA-containing transformants were reintroduced into ryegrass seedlings and expression of GUS visualized in vivo, demonstrating that 187BB can be used as a surrogate host to introduce foreign genes into perennial ryegrass.(ABSTRACT TRUNCATED AT 250 WORDS)

Acremonium↗
PubMed1991

Effects of remoxipride on measures of psychological performance in healthy volunteers.

The acute psychomotor effects after oral doses of 30, 60 and 120 mg remoxipride, a new selective D2 receptor blocker, and placebo were investigated in a double-blind crossover study in 11 healthy male volunteers. Two out of the first three subjects given 120 mg remoxipride experienced marked akathisia, and therefore no subsequent subjects were given this dose. There were no other clearly drug-related adverse effects reported below 120 mg, although restlessness was reported at 60 mg. Remoxipride was associated with increases in error scores on a continuous attention task and on auditory vigilance, and with a reduction in critical flicker frequency, suggesting a decrease in arousal level. There were no significant changes in psychomotor measures such as choice reaction time, decision making time, or body sway. Subjective assessments using visual analogue scales showed a slight dose-related increase in drowsiness, while the calm-excited scale showed a small change in the excited direction with 30 mg only. The peak effects were at 4-6 h after drug intake, which was later than expected from previous pharmacokinetic data. These results indicate that remoxipride may have a slight depressant effect in the dose-range used. The pattern of changes is consistent with current theories on the role of dopamine in attention and arousal, and with the effects of other neuroleptics. It differs, however, from tranquilisers such as the benzodiazepines, which show a more global pattern of effects.

Adult↗
PubMed1991

Expression and nucleotide sequence of the Clostridium acetobutylicum beta-galactosidase gene cloned in Escherichia coli.

A gene library for Clostridium acetobutylicum NCIB 2951 was constructed in the broad-host-range cosmid pLAFR1, and cosmids containing the beta-galactosidase gene were isolated by direct selection for enzyme activity on X-Gal (5-bromo-4-chloro-3-indolyl-beta-D-galactoside) plates after conjugal transfer of the library to a lac deletion derivative of Escherichia coli. Analysis of various pSUP202 subclones of the lac cosmids on X-Gal plates localized the beta-galactosidase gene to a 5.1-kb EcoRI fragment. Expression of the Clostridium beta-galactosidase gene in E. coli was not subject to glucose repression. By using transposon Tn5 mutagenesis, two gene loci, cbgA (locus I) and cbgR (locus II), were identified as necessary for beta-galactosidase expression in E. coli. DNA sequence analysis of the entire 5.1-kb fragment identified open reading frames of 2,691 and 303 bp, corresponding to locus I and locus II, respectively, and in addition a third truncated open reading frame of 825 bp. The predicted gene product of locus I, CbgA (molecular size, 105 kDa), showed extensive amino acid sequence homology with E. coli LacZ, E. coli EbgA, and Klebsiella pneumoniae LacZ and was in agreement with the size of a polypeptide synthesized in maxicells containing the cloned 5.1-kb fragment. The predicted gene product of locus II, CbgR (molecular size, 11 kDa) shares no significant homology with any other sequence in the current DNA and protein sequence data bases, but Tn5 insertions in this gene prevent the synthesis of CbgA. Complementation experiments indicate that the gene product of cbgR is required in cis with cbgA for expression of beta-galactosidase in E. coli.

Amino Acid Sequence↗
PubMed1991

Exopolysaccharide mutants of Rhizobium loti are fully effective on a determinate nodulating host but are ineffective on an indeterminate nodulating host.

By Tn5 mutagenesis of Rhizobium loti PN184 (NZP2037 str-1) and selection for nonfluorescence of colonies on Calcofluor agar, eight independently generated expolysaccharide (EPS) mutants (three smooth and five rough) were isolated. The parent strain, PN184, was found to produce an acidic EPS. This EPS was produced. with reduced O acetylation, by the smooth EPS mutants but not by the rough EPS mutants. Lipopolysaccharide was isolated from all mutants and was identical to that of PN184 as defined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. All mutants were resistant to lysis by R. loti bacteriophage phi 2037/1. Cosmids that complemented the mutations in the rough EPS mutants were isolated from a pLAFR1 gene library of NZP2037 by complementation of the nonfluorescent phenotype. The genes identified were shown to be unlinked and located on the chromosome. All mutants were fully effective when inoculated onto Lotus pedunculatus, a determinate nodulating host, but were ineffective, inducing the formation of very small nodules or tumorlike growths, when inoculated onto Leucaena leucocephala, an indeterminate nodulating host. These results, obtained in an isogenic Rhizobium background, support suggestions that acidic EPS is required for effective nodulation of indeterminate nodulating legumes but is not required for effective nodulation of determinate nodulating legumes.

Cosmids↗
PubMed1990

A comparison of the CNS effects of enprofylline and theophylline in healthy subjects assessed by performance testing and subjective measures.

1. The effects of intravenous infusions of enprofylline, theophylline, and placebo on subjective ratings and on psychological test performance were studied in a double-blind crossover experiment in 12 healthy subjects who abstained from caffeine throughout the experimental procedures. 2. Mean plasma concentrations of enprofylline were: mean 2.9 mg l-1 (range 1.9-3.4). Those for theophylline were: mean 12.1 mg l-1 (range 9.0-14.4). 3. Performance on the auditory vigilance task showed a significant improvement with theophylline compared with both enprofylline and placebo. The correct detection rates (out of 90) were 50.3, 43.4 and 39.1 respectively. A similar effect was seen with finger tapping rates: 404, 394 and 390 taps min-1 respectively. Other measures showed no significant effects, although choice reaction time showed a trend towards faster responses with theophylline. 4. Subjective ratings showed that subjects were significantly more alert with theophylline than with enprofylline. Subjects reported themselves as significantly more dizzy and ill with both active drugs compared with placebo. 5. These results suggest that emprofylline largely lacks the CNS stimulant effects of theophylline, but that the incidence of other unwanted effects of the drugs may be similar.

Acoustic Stimulation↗
PubMed1979

The biosynthesis of nitrogenase MoFe protein polypeptides in free-living cultures of Rhizobium japonicum.

The biosynthesis of the constituent polypeptides of nitrogenase component I (Rj 1) in free-living cultures of Rhizobium japonicum (strain 110) was investigated under different growth conditions. Cells were pulse-labelled and the proteins analysed by one and two-dimensional gel electrophoresis. The positions of the constituent Rj 1 polypeptides were identified by co-electrophoresis with purified Rj 1 isolated from bacteroids of soybean nodules, and by comparison with an immunoprecipitate from a culture induced for nitrogenase. The synthesis of the proteins preceded any detectable enzyme activity and increased with time, reaching a maximum after 3 days. At this time, between 6 and 8% of the total sodium dodecyl sulfate-soluble protein synthesized was Rj 1. Exposure to air led to a dramatic decrease in the rate of Rj 1 synthesis, with almost complete regression after 20 min. In the presence of KNO3, there was no nitrogenase activity, but the proteins were present in similar amounts (7%) as the control culture. When mannitol and glycerol were used as the sole carbon sources, the amount of Rj 1 synthesized was extremely low.

Gluconates↗
PubMed1979

Pharmacokinetic and clinical pharmacological studies with mepivacaine and prilocaine.

The tolerance and pharmacokinetic properties of mepivacaine and prilocaine were compared following i.v. infusion of 250 mg (0.88 and 0.97 mmol respectively) of each drug in five healthy volunteers. Side-effects were minor and occurred in only two subjects during the infusion of mepivacaine. Plasma concentrations of mepivacaine were greater in each subject than the corresponding values for prilocaine. The elimination half-life of mepivacaine was generally longer than that for prilocaine, whereas the total body clearance of prilocaine was consistently greater than the corresponding value for mepivacaine. For each subject the clearance of prilocaine substantially exceeded normal heptic blood flow and therefore an extra-hepatic site of metabolism of prilocaine has been postulated.

Adult↗
PubMed1979

Cardiovascular effects of prenalterol (H133/22) in normal man.

1 Prenalterol, (S-(-)-1-(4 hydroxyphenoxy)-3-isopropylaminopropanol-2 hydrochloride) a cardio-selective beta-adrenergic receptor agonist, was infused intravenously into six normal male volunteers to determine the cardiovascular effects of this drug. 2 On different occasions, each volunteer received a placebo infusion, an infusion of 0.5 mg prenalterol and an infusion of 1 mg prenalterol. Cardiac output (impedance cardiography), arterial pressure (sphygmomanometry), heart rate and ECG were measured throughout. 3 Prenalterol produced a statistically significant increase in cardiac output and at the end of the infusion this increase was 24% with 0.5 mg and 29% with 1 mg, mainly due to an increase in stroke volume (18% and 17%) with a lesser change in heart rate (+2 and +7 beats/min). Pulse pressure increased but mean arterial pressure showed little change. Peripheral resistance fell by 18% and 20%. As indicated by systolic time indices myocardial contractility increased. 4 Prenalterol at plasma concentrations in excess of 20 nmol l-1 produced significant inotropic effects but did not markedly increase heart rate at concentrations of 60 nmol l-1.

Adrenergic beta-Agonists↗
PubMed1979

Effect of cyclic guanosine 3',5'-monophosphate on nitrogen fixation in Rhizobium japonicum.

The addition of exogenous cyclic guanosine 3',5'-monophosphate (cGMP) at a concentration of 0.1 mM to a free-living culture of Rhizobium japonicum 3I1b110 was found to completely inhibit the expression of nitrogenase activity and markedly inhibit the expression of hydrogenase and nitrate reductase activities. The effect was specific for cGMP. Experiments on the in vivo incorporation of radioactive methionine and subsequent analysis of the labeled proteins on polyacrylamide gels showed that the biosynthesis of nitrogenase polypeptides was inhibited. It appears that the time of addition of cGMP is important since the effect was only seen during the early stages of nif gene expression. The intracellular level of cGMP was found to respond to physiological changes in the cell, and there was a fall in cGMP concentrations when nitrogenase was induced. Microaerophilic-aerobic shift experiments showed that intracellular levels increased from 0.25 pmol/mg of cell protein under microaerophilic conditions to 2.6 pmol/mg of cell protein under aerobic conditions, suggesting that the cellular pool size of cGMP may be under redox control.

Cyclic GMP↗