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Biomedical subjects

G M Cook

Publications and source records attributed to G M Cook.

At least 19 recordsLinked to original sources
PubMed1997

Roles of RpoS (sigmaS), IHF and ppGpp in the expression of the hmp gene encoding the flavohemoglobin (Hmp) of Escherichia coli K-12.

The Escherichia coli K-12 gene hmp encodes the flavohemoglobin Hmp. A hmp promoter phi(hmp-lacZ)-operon fusion was constructed in the chromosome and its activity measured during the growth cycle. Logarithmically growing cultures had low levels of phi(hmp-lacZ) expression, which increased two-fold at the onset of stationary phase in rich medium. The effect was abolished in a strain carrying a null allele of the gene rpoS encoding the stationary phase-specific sigma subunit of RNA polymerase sigmaS. A himA mutation resulted in a 1.5-fold increase in expression of phi(hmp-lacZ) but did not affect growth phase-dependent regulation. A single transcriptionial start site was found for hmp, located 38 bp upstream of the initiation codon. Putative Fnr boxes at positions -2 to +11 occur in the hmp promoter region.

Amino Acid Sequence↗
PubMed1997

Surround repulsion of spinal sensory axons in higher vertebrate embryos.

We have tested whether the orientation of axons sprouting from bipolar dorsal root ganglion neurons is influenced by diffusible cues from surrounding tissues. Surface ectoderm, dermomyotome, and notochord exert strong chemorepulsion on axons growing in collagen gels, operating at separations beyond those found in vivo and active in cocultures of chick and mouse tissues. Basal and alar plates of the neural tube are devoid of activity, as is the posterior-half-sclerotome, which repels in a contact-dependent manner. When ganglia are sandwiched between dermomyotome and notochord placed at a distance, axon growth is channeled in a bipolar trajectory. These results show that gradients of diffusible repulsion molecules flanking axon pathways can generate linear patterns of axon growth. We suggest that such "surround repulsion" may function generally, in concert with contact-dependent guidance mechanisms, to guide axons in the developing nervous system.

Animals↗
PubMed1997

Paraquat regulation of hmp (flavohemoglobin) gene expression in Escherichia coli K-12 is SoxRS independent but modulated by sigma S.

We report the first example of a gene, hmp, encoding a soluble flavohemoglobin in Escherichia coli K-12, which is up-regulated by paraquat in a SoxRS-independent manner. Unlike what is found for other paraquat-inducible genes, high concentrations of paraquat (200 microM) were required to increase the level of hmp expression, and maximal induction was observed only after 20 min of exposure to paraquat. Neither a mutation in soxS nor one in soxR prevented the paraquat-dependent increase in phi(hmp-lacZ) expression, but either mutant allele delayed full expression of phi(hmp-lacZ) activity after paraquat addition. Induction of hmp by paraquat was demonstrated in aerobically grown cultures during exponential growth and the stationary phase, thus revealing two Sox-independent regulatory mechanisms. Induction of hmp by paraquat in the stationary phase was dependent on the global regulator of stationary-phase gene expression, RpoS (sigma S). However, a mutation in rpoS did not prevent an increase in hmp expression by paraquat in exponentially growing cells. Induction of sigma S in the exponential phase by heat shock also induced phi(hmp-lacZ) expression in the presence of paraquat, supporting the role of sigma S in one of the regulatory mechanisms. Mutations in oxyR or rob, known regulators of several stress promoters in E. coli, had no effect on the induction of hmp by paraquat. Other known superoxide-generating agents (plumbagin, menadione, and phenazine methosulfate) were not effective in inducing hmp expression.

Bacterial Proteins↗
PubMed1996

Inducer expulsion is not a determinant of diauxic growth in Streptococcus bovis.

When Streptococcus bovis JB1 was repeatedly transferred in a medium that contained the non-metabolizable glucose analog, 2-deoxyglucose, it lost its phosphotransferase system (PTS) for glucose but was still able to take up glucose via a facilitated diffusion mechanism. The wild type (JB1) had an inducible enzyme II lactose, but the mutant (JB1(2DG)) had a constitutive lactose PTS. JB1(2DG) was no longer able to exclude lactose when it was provided with glucose, but it retained its ability to expel a non-metabolizable lactose analog. Because JB1(2DG) could utilize glucose and lactose simultaneously and grow in a non-diauxic fashion, it appeared that inducer expulsion was not an important catabolite regulatory mechanism. Based on these results, inducer expulsion may be an artifact of non-metabolizable sugars.

Biological Transport, Active↗
PubMed1996

Characterization of a new obligately anaerobic thermophile, Thermoanaerobacter wiegelii sp. nov.

An obligately anaerobic, extremely thermophilic Thermoanaerobacter species was isolated from a freshwater pool formed from a geothermally heated (56 to 69 degrees C) water outlet in Government Gardens, Rotorua, New Zealand. This organism was a spore-forming, gram-negative, rod-shaped bacterium. Strain Rt8.B1T (= DSM 10319T) (T = type strain) fermented a wide variety of mono-, di-, and polysaccharides and produced ethanol, acetate, lactate, propionate, and hydrogen. Sugar alcohols were also fermented, but organic acids and amino acids were not utilized. On the basis of its morphological characteristics, DNA G + C content, obligately anaerobic, thermophilic, polysaccharolytic nature, and levels of 16S rRNA sequence homology, we propose that strain Rt8.B1T should be classified in the genus Thermoanaerobacter as a new species, Thermoanaerobacter wiegelii.

Bacteria, Anaerobic↗
PubMed1996

Nisin stimulates oxygen consumption by Staphylococcus aureus and Escherichia coli.

Nisin stimulated oxygen consumption by nongrowing, glucose-metabolizing Staphylococcus aureus and Escherichia coli cells, indicating a protonophore mode of action. A similar stimulation in E. coli cells osmotically stressed to disrupt the outer cell membrane confirmed the cytoplasmic membrane as the site of nisin action and showed that nisin uptake was not prevented by the outer membrane.

Escherichia coli↗
PubMed1995

Repulsive and inhibitory signals.

Repulsive or inhibitory interactions between growth cones and their environment are now widely implicated in neural development and regeneration. Over the past year, descriptive studies of the various neuronal systems in which repulsion may participate have clarified its biology. Molecular and genetic studies have also provided the necessary entry point for further experimental manipulations, and are beginning to yield important clues regarding the function of repulsion in vivo. Although candidate second messengers underlying the growth cone response have been identified, they have yet to be incorporated into a comprehensive mechanism.

Animals↗
PubMed1995

Regulation of the lactose phosphotransferase system of Streptococcus bovis by glucose: independence of inducer exclusion and expulsion mechanisms.

Streptococcus bovis had a diauxic pattern of glucose and lactose utilization, and both of these sugars were transported by the sugar phosphotransferase system (PTS). Lactose catabolism was inducible, and S. bovis used the tagatose pathway to ferment lactose. Since a mutant that was deficient in glucose PTS activity transported lactose as fast as the wild-type, it appeared that S. bovis has separate enzyme IIs for glucose and lactose. The nonmetabolizable glucose analogue 2-deoxyglucose (2-DG) was a noncompetitive inhibitor of methyl beta-D-thiogalactopyranoside (TMG) transport, and cells that were provided with either glucose or 2-DG were unable to transport TMG or lactose. Because the glucose-PTS-deficient mutant could ferment glucose, but could not exclude TMG, it appeared that enzyme IIGlc rather than glucose catabolism per se was the critical feature of inducer exclusion. Cells that had accumulated TMG as TMG 6-phosphate expelled free TMG when glucose was added, but 2-DG was unable to cause TMG expulsion. The glucose-PTS-deficient mutant could still expel TMG in the presence of exogenous glucose. Membrane vesicles also exhibited glucose-dependent TMG exclusion and TMG expulsion. Membrane vesicles that were electroporated with phosphoenolpyruvate (PEP) and HPr retained TMG for more than 3 min, but vesicles that were electroporated with PEP plus HPr and fructose 1,6-diphosphate (FDP) (or glycerate 2-phosphate) lost their ability to retain TMG. Because FDP was able to trigger the ATP-dependent phosphorylation of HPr, it appeared that inducer expulsion was mediated by an FDP-activated protein kinase.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Proteins↗
PubMed1995

Properties of two sugar phosphate phosphatases from Streptococcus bovis and their potential involvement in inducer expulsion.

Streptococcus bovis possesses two sugar phosphate phosphatases (Pases). Pase I is a soluble enzyme that is inhibited by the membrane fractions from lactose-grown cells and is insensitive to activation by S46D HPr, an analog of HPr(ser-P) of the sugar phosphotransferase system. Pase II is a membrane-associated enzyme that can be activated 10-fold by S46D HPr, and it appears to play a role in inducer expulsion.

Bacterial Proteins↗
PubMed1995

Energetics of bacterial growth: balance of anabolic and catabolic reactions.

Biomass formation represents one of the most basic aspects of bacterial metabolism. While there is an abundance of information concerning individual reactions that result in cell duplication, there has been surprisingly little information on the bioenergetics of growth. For many years, it was assumed that biomass production (anabolism) was proportional to the amount of ATP which could be derived from energy-yielding pathways (catabolism), but later work showed that the ATP yield (YATP) was not necessarily a constant. Continuous-culture experiments indicated that bacteria utilized ATP for metabolic reactions that were not directly related to growth (maintenance functions). Mathematical derivations showed that maintenance energy appeared to be a growth rate-independent function of the cell mass and time. Later work, however, showed that maintenance energy alone could not account for all the variations in yield. Because only some of the discrepancy could be explained by the secretion of metabolites (overflow metabolism) or the diversion of catabolism to metabolic pathways which produced less ATP, it appeared that energy-excess cultures had mechanisms of spilling energy. Bacteria have the potential to spill excess ATP in futile enzyme cycles, but there has been little proof that such cycles are significant. Recent work indicated that bacteria can also use futile cycles of potassium, ammonia, and protons through the cell membrane to dissipate ATP either directly or indirectly. The utility of energy spilling in bacteria has been a curiosity. The deprivation of energy from potential competitors is at best a teleological explanation that cannot be easily supported by standard theories of natural selection. The priming of intracellular intermediates for future growth or protection of cells from potentially toxic end products (e.g., methylglyoxal) seems a more plausible explanation.

Adenosine Triphosphate↗
PubMed1994

Alternative strategies of 2-deoxyglucose resistance and low affinity glucose transport in the ruminal bacteria, Streptococcus bovis and Selenomonas ruminantium.

Streptococcus bovis and Selenomonas ruminantium grew in the presence of the glucose analog, 2-deoxyglucose (2-DG), but the cells no longer had high affinity glucose transport. In S. bovis, 2-DG resistance was correlated with a decrease in phosphoenolpyruvate (PEP)-dependent glucose phosphotransferase (PTS) activity. The 2-DG-selected S. bovis cells relied solely upon a low affinity, facilitated diffusion mechanism of glucose transport and a 2-DG-resistant glucokinase (ATP-dependent). The glucokinase activity of S. ruminantium was competitively inhibited by 2-DG, and the 2-DG selected cells continued to use PEP-dependent PTS as a mechanism of glucose transport. In this latter case, the 2-DG selected cells switched from a mannosephosphotransferase (enzyme II) that phosphorylated glucose, mannose, and 2-DG, but not alpha-methylglucose to a glucosephosphotransferase (enzyme II) that phosphorylated glucose and alpha-methylglucoside but not 2-DG or mannose. The glucosephosphotransferase (enzyme II) had a very low affinity for glucose and the transport kinetics were similar to the facilitated diffusion system of S. bovis.

Animals↗
PubMed1994

Swallowing in Alzheimer's disease.

Using a prospective case series design, we examined the incidence of oropharyngeal swallowing abnormalities in 25 patients with moderate or severe Alzheimer's disease by videofluoroscopy. Aspiration occurred in 6 of 25 (28.6%). Only four patients showed unequivocally normal performance. Exploratory statistical analyses showed that swallowing abnormalities associated significantly with duration of dementia, eating dependency, and abnormal oral praxis. We observed a trend toward a higher incidence of aspiration in patients with more severe dementia. We conclude that oropharyngeal swallowing abnormalities, including aspiration, are more prevalent in patients with Alzheimer's disease than in normal elderly individuals.

Aged↗
PubMed1994

Emendation of the description of Acidaminococcus fermentans, a trans-aconitate- and citrate-oxidizing bacterium.

Ruminal fluid which was enriched with trans-aconitate yielded a gram-negative diplococcus (strain AO) which was identified by 16S ribosomal DNA sequence analysis as Acidaminococcus fermentans. In contrast to the original description, the A. fermentans type strain and strain AO were found to utilize citrate as an energy source and to produce hydrogen and hydrogen sulfide. The descriptions of the genus and species are emended accordingly.

Aconitic Acid↗
PubMed1994

Energy-spilling reactions of Streptococcus bovis and resistance of its membrane to proton conductance.

Glucose-excess cultures of Streptococcus bovis consumed glucose faster than the amount that could be explained by growth or maintenance, and nongrowing chloramphenicol-treated cells had a rate of glucose consumption that was 10-fold greater than the maintenance rate. Because N,N-dicyclohexylcarbodiimide, an inhibitor of the membrane-bound F1F0 ATPase, eliminated the nongrowth energy dissipation (energy spilling) without a decrease in ATP and the rate of energy spilling could be increased by the protonophore 3,3',4',5-tetrachlorosalicylanilide, it appeared that a futile cycle of protons through the cell membrane was responsible for most of the energy spilling. When the rate of energy spilling was decreased gradually with iodoacetate, there was only a small decrease in the phosphorylation potential (delta G'p) and the theoretical estimate of H+ per ATP decreased from 4.2 to 3.6. On the bases of this ratio of H+ to ATP and the rate of ATP production, the flux of protons (amperage) across the cell membrane was directly proportional to the rate of energy spilling. Amperage values estimated from delta G'p were, however, nearly twice as great as values which were estimated from the heat production (delta H) of the cells [amperage = (0.38 x wattage)/delta p]. The last comparison indicated that only a fraction of the delta G of ATP hydrolysis was harvested by the F1F0 ATPase to pump protons. Both estimates of amperage indicated that the resistance of the cell membrane to proton conductance was inversely proportional to the log of the energy-spilling rate.

Adenosine Triphosphate↗