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Biomedical subjects

S Silver

Publications and source records attributed to S Silver.

At least 55 records · Page 3Linked to original sources
PubMed1995

Ion efflux systems involved in bacterial metal resistances.

Studying metal ion resistance gives us important insights into environmental processes and provides an understanding of basic living processes. This review concentrates on bacterial efflux systems for inorganic metal cations and anions, which have generally been found as resistance systems from bacteria isolated from metal-polluted environments. The protein products of the genes involved are sometimes prototypes of new families of proteins or of important new branches of known families. Sometimes, a group of related proteins (and presumedly the underlying physiological function) has still to be defined. For example, the efflux of the inorganic metal anion arsenite is mediated by a membrane protein which functions alone in Gram-positive bacteria, but which requires an additional ATPase subunit in some Gram-negative bacteria. Resistance to Cd2+ and Zn2+ in Gram-positive bacteria is the result of a P-type efflux ATPase which is related to the copper transport P-type ATPases of bacteria and humans (defective in the human hereditary diseases Menkes' syndrome and Wilson's disease). In contrast, resistance to Zn2+, Ni2+, Co2+ and Cd2+ in Gram-negative bacteria is based on the action of proton-cation antiporters, members of a newly-recognized protein family that has been implicated in diverse functions such as metal resistance/nodulation of legumes/cell division (therefore, the family is called RND). Another new protein family, named CDF for 'cation diffusion facilitator' has as prototype the protein CzcD, which is a regulatory component of a cobalt-zinc-cadmium resistance determinant in the Gram-negative bacterium Alcaligenes eutrophus. A family for the ChrA chromate resistance system in Gram-negative bacteria has still to be defined.

ATP-Binding Cassette Transporters↗
PubMed1995

CadC, the transcriptional regulatory protein of the cadmium resistance system of Staphylococcus aureus plasmid pI258.

The CadC protein from the cadA cadmium resistance operon of Staphylococcus aureus plasmid pI258 regulates transcription of this system in vitro. The CadC protein was overproduced in Escherichia coli cells and partially purified. Gel shift assays of the proposed cadA operator/promoter region DNA showed specific association with the CadC protein. Control arsenic resistance operator/promoter DNA from the same plasmid was not shifted by the CadC protein. Cd2+, Bi3+, and Pb2+ caused the release of CadC from DNA in gel retardation assays. DNase I footprinting measurements showed that the CadC protein specifically associated with and protected a region of operator/promoter DNA from nucleotide positions -7 to +14 relative to the start point of mRNA synthesis. Runoff transcription assays with the operator/promoter region of DNA (plus the first 69 nucleotides of the cadC gene) and purified E. coli RNA polymerase gave an mRNA product of the predicted size. Added CadC protein inhibited transcription in vitro.

Amino Acid Sequence↗
PubMed1995

Visual evoked potential abnormalities in jaundiced Gunn rats treated with sulfadimethoxine.

The manifestations of bilirubin encephalopathy include disturbances in the visual pathway (visual gaze paralysis and distorted visual perception). In the young jaundiced Gunn rat (jj) model of hyperbilirubinemia, significant differences in visual evoked potential (VEP) patterns have been recorded during development. In the present study, the effects of sulfadimethoxine (SDM) on VEP and electroretinogram (ERG) were examined in 3-wk-old jj rats. This drug displaces bilirubin from its albumin binding sites in the circulation, shifting it into tissues including the brain. Marked latency prolongations (11-20%) and reduced amplitudes (20-64%) were observed in the different wave components of the VEP. These changes were evident as early as 2 h after injection of the drug and persisted thereafter for another 4 h. On the other hand, ERG changes (significant prolongation of wave b) became apparent in these animals only 6 h after SDM injection. These results suggest that, although some changes in the retina may occur after a massive entry of bilirubin into the nervous system, the primary damage in the visual pathway after bilirubin exposure is probably beyond the retina.

Animals↗
PubMed1995

Contribution of asphyxia to the induction of hearing impairment in jaundiced Gunn rats.

OBJECTIVES: This study was designed to determine whether asphyxia contributes to the induction of hearing impairment during neonatal jaundice. METHODS: Asphyxia was induced in jaundiced and nonjaundiced Gunn rats on postnatal days 1 (low bilirubin levels) and 10 (elevated bilirubin levels). Auditory nerve-brainstem evoked response thresholds were assessed in 21- and 28-day and 3-month-old rats. RESULTS: Asphyxia by itself or jaundice by itself did not lead to any type of hearing impairment. However, the combination of both high plasma bilirubin levels and asphyxia in 10-day-old rats but not in 1-day-old rats was accompanied by a progressive hearing loss in these rats. CONCLUSIONS: The contributory effect of asphyxia on neonatal jaundice may have important clinical relevance if asphyxia, for example, respiratory distress, accompanies neonatal jaundice.

Animals↗
PubMed1994

Arsenate reductase of Staphylococcus aureus plasmid pI258.

Arsenate reductase encoded by Staphylococcus aureus arsenic-resistance plasmid pI258 was overproduced in Escherichia coli and purified. The purified enzyme reduced radioactive arsenate to arsenite when coupled to thioredoxin, thioredoxin reductase, and NADPH. NADPH oxidation coupled to arsenate reduction also required thioredoxin and thioredoxin reductase. Glutaredoxin and reduced glutathione did not stimulate arsenate reduction. NADPH oxidation showed Michaelis-Menten kinetics with a Km of 1 microM AsO4(3-) and an apparent Vmax of 200 nmol/min per mg of protein. At high substrate concentration (above 1 mM AsO4(3-), a secondary rise in the reaction rate was observed, with a Km of 2 mM and an apparent Vmax of 450 nmol/min per mg of protein. This secondary rise also occurred upon addition of phosphate or nitrate (which were not substrates for the enzyme). Arsenite (the product of the enzyme), tellurite, and antimonite [Sb(III)] were inhibitors. Selenate (but not selenite or sulfate) was a substrate for reductase-dependent NADPH oxidation, with an apparent Km of 13 mM SeO4(2-). Arsenate reductase was purified as a monomer of 14.5 kDa, consistent with the DNA sequence. Electrospray mass spectrometry showed two molecular masses of 14,810.5 and 14,436.0 Da, suggesting that 70% of the purified protein lacked the N-terminal three amino acids; HPLC coupled to electrospray mass spectroscopy of protease digest products confirmed this conclusion and verified the entire amino acid sequence.

Adenosine Triphosphatases↗
PubMed1994

The Numbing Scale: psychometric properties, a preliminary report.

This study explored the psychometric properties of a new self-report instrument, The Glover Numbing Scale. The scale measures a variety of behaviors reported by individuals experiencing an inability to access feelings other than hostility and rage. The scale was administered to inpatient Vietnam combat veterans with post-traumatic stress disorder (PTSD, n = 323), PTSD diagnosed Veterans Affairs (VA) outpatient and veterans' outreach center veterans (n = 208), two Vietnam veteran noncombat groups (n = 45), two psychiatric noncombat controls (anxiety disorder, n = 40; major depressive disorder, n = 31), and a nonpsychiatric never-in-Vietnam veteran control group (n = 48). Reliability information suggested that the scale was internally consistent with good test-retest correlations. Convergent and discriminant validations were assessed based on the pattern of the scale's correlations with relevant Minnesota Multiphasic Personality Inventory (MMPI) scales. The contrasting pattern of correlations provided by a subgroup of veterans who reported always feeling dead or shut down was highlighted. Principal component analysis resulted in a five factor solution that provided evidence for the scale's factorial validity. Numbing Scale scores discriminated levels of psychopathology within the veteran population. PTSD outreach center veterans' sum scores and item scores on the Numbing Scale were more similar to responses of anxiety disorder patients than to major depressive disorder patients. Overall, the findings strongly support the clinical application of the Numbing Scale.

Adult↗
PubMed1994

Resistance to arsenic compounds in microorganisms.

Arsenic ions, frequently present as environmental pollutants, are very toxic for most microorganisms. Some microbial strains possess genetic determinants that confer resistance. In bacteria, these determinants are often found on plasmids, which has facilitated their study at the molecular level. Bacterial plasmids conferring arsenic resistance encode specific efflux pumps able to extrude arsenic from the cell cytoplasm thus lowering the intracellular concentration of the toxic ions. In Gram-negative bacteria, the efflux pump consists of a two-component ATPase complex. ArsA is the ATPase subunit and is associated with an integral membrane subunit, ArsB. Arsenate is enzymatically reduced to arsenite (the substrate of ArsB and the activator of ArsA) by the small cytoplasmic ArsC polypeptide. In Gram-positive bacteria, comparable arsB and arsC genes (and proteins) are found, but arsA is missing. In addition to the wide spread plasmid arsenic resistance determinant, a few bacteria confer resistance to arsenite with a separate determinant for enzymatic oxidation of more-toxic arsenite to less-toxic arsenate. In contrast to the detailed information on the mechanisms of arsenic resistance in bacteria, little work has been reported on this subject in algae and fungi.

Arsenic↗
PubMed1994

Molecular analysis of mercury-resistant Bacillus isolates from sediment of Minamata Bay, Japan.

Bacillus isolates from Minamata Bay sediment were selected for the ability to volatilize mercury from a range of organomercurials (including methylmercury). Chromosomal DNA from 74 of 78 such strains hybridized with the mer mercury resistance operon DNA from marine Bacillus sp. strain RC607 (Y. Wang, M. Moore, H. S. Levinson, S. Silver, C. Walsh, and I. Mahler, J. Bacteriol. 171:83-92, 1989). The most frequent classes with regard to restriction nuclease site maps of the mer operon for the new isolates were identical to or closely related to the mer determinant of strain RC607. PCR amplification analysis with primers designed from the strain RC607 mer operon gave products of precisely the predicted size with the 74 Minamata Bay isolates.

Amino Acid Sequence↗
PubMed1994

Newer systems for bacterial resistances to toxic heavy metals.

Bacterial plasmids contain specific genes for resistances to toxic heavy metal ions including Ag+, AsO2-, AsO4(3-), Cd2+, Co2+, CrO4(2-), Cu2+, Hg2+, Ni2+, Pb2+, Sb3+, and Zn2+. Recent progress with plasmid copper-resistance systems in Escherichia coli and Pseudomonas syringae show a system of four gene products, an inner membrane protein (PcoD), an outer membrane protein (PcoB), and two periplasmic Cu(2+)-binding proteins (PcoA and PcoC). Synthesis of this system is governed by two regulatory proteins (the membrane sensor PcoS and the soluble responder PcoR, probably a DNA-binding protein), homologous to other bacterial two-component regulatory systems. Chromosomally encoded Cu2+ P-type ATPases have recently been recognized in Enterococcus hirae and these are closely homologous to the bacterial cadmium efflux ATPase and the human copper-deficiency disease Menkes gene product. The Cd(2+)-efflux ATPase of gram-positive bacteria is a large P-type ATPase, homologous to the muscle Ca2+ ATPase and the Na+/K+ ATPases of animals. The arsenic-resistance system of gram-negative bacteria functions as an oxyanion efflux ATPase for arsenite and presumably antimonite. However, the structure of the arsenic ATPase is fundamentally different from that of P-type ATPases. The absence of the arsA gene (for the ATPase subunit) in gram-positive bacteria raises questions of energy-coupling for arsenite efflux. The ArsC protein product of the arsenic-resistance operons of both gram-positive and gram-negative bacteria is an intracellular enzyme that reduces arsenate [As(V)] to arsenite [As(III)], the substrate for the transport pump. Newly studied cation efflux systems for Cd2+, Zn2+, and Co2+ (Czc) or Co2+ and Ni2+ resistance (Cnr) lack ATPase motifs in their predicted polypeptide sequences. Therefore, not all plasmid-resistance systems that function through toxic ion efflux are ATPases. The first well-defined bacterial metallothionein was found in the cyanobacterium Synechococcus. Bacterial metallothionein is encoded by the smtA gene and contains 56 amino acids, including nine cysteine residues (fewer than animal metallothioneins). The synthesis of Synechococcus metallothionein is regulated by a repressor protein, the product of the adjacent but separately transcribed smtB gene. Regulation of metallothionein synthesis occurs at different levels; quickly by derepression of repressor activity, or over a longer time by deletion of the repressor gene at fixed positions and by amplification of the metallothionein DNA region leading to multiple copies of the gene.

Alcaligenes↗
PubMed1994

Vulnerability Scale: a preliminary report of psychometric properties.

This work describes assessment of the psychometric properties of a self-report instrument, the Glover Vulnerability Scale. This scale was administered to a total of 11 groups (N = 695). Six of the groups were Vietnam combat veterans diagnosed as having Posttraumatic Stress Disorder (n = 531). The estimate of internal consistency was .88; the test-retest correlation over 4 wk. was .81. Convergent and discriminant validations were satisfactory based on the pattern of the scale's correlations with relevant MMPI subscales and demographic data. Scale scores also discriminated levels of functioning within the population diagnosed with Posttraumatic Stress Disorder and discriminated veterans diagnosed with Posttraumatic Stress Disorder from patients with major depressive disorder and anxiety disorder. Principal component factor analysis gave a 4-factor solution: social comfort, vulnerability, paranoia, and family trust. Over-all, the findings strongly support the clinical application of the Vulnerability Scale.

Adult↗
PubMed1994

Lessons from child of water.

This chapter examines the perceptions and treatment of psychological combat reactions by American Indians. My goal is to provide the reader with an introduction to the clinical implications of these perceptions and treatment in order to encourage a closer examination of what American Indian healers have to offer mental health professionals trained in the mainstream (what I will refer to as Anglo) psychological tradition. To do this we shall briefly examine how American Indians regard war and the role of warriors, for this cultural perception influences how combat reactions such as posttraumatic stress disorder symptoms are perceived and treated. Regardless of the value of what we might learn from American Indian culture, it does not matter what they say if we will not hear. It is necessary to consider attitudes typically held toward the concepts and techniques of American Indian healing practices if we wish for this examination to be more than an anthropological exposition, and have clinical value for Anglo mental health professionals.

Adaptation, Psychological↗
PubMed1993

luxAB gene fusions with the arsenic and cadmium resistance operons of Staphylococcus aureus plasmid pI258.

pC101, a novel shuttle vector between Escherichia coli and Staphylococcus aureus carrying the lux genes encoding luciferase from Vibrio harveyi, selectable ampicillin and chloramphenicol markers and origins of replication for Gram-negative and Gram-positive bacteria has been constructed. The inducibility of the arsenic and cadmium operon from S. aureus plasmid pI258 to different ions has been tested in E. coli and in S. aureus with two fusions in pC101: an arsB-luxAB and a cadA-luxAB transcriptional gene fusion. Patterns of induction are influenced by the host strain and are slightly different from previous reports using the blaZ gene as reporter gene.

Adenosine Triphosphatases↗
PubMed1993

Broadly neutralizing monoclonal antibodies to the V3 region of HIV-1 can be elicited by peptide immunization.

The third hypervariable region (V3) of the HIV-1 envelope gp120 protein contains the principal neutralizing domain. Most neutralizing antibodies directed toward this region are very type-specific. Conserved sequences do exist within this region, however, and may prove useful in developing vaccines and therapeutic monoclonal antibodies (MABs) capable of targeting diverse HIV-1 isolates. We have used synthetic peptides containing conserved V3 sequences as immunogens to produce a panel of neutralizing MABs. The characterization of these MABs is described here. In addition, a series of in vitro assays has been developed that may be useful in predicting the neutralization potential of individual antibodies.

Amino Acid Sequence↗
PubMed1993

Expansion of human bone marrow progenitor cells in a high cell density continuous perfusion system.

We describe here a continuous perfusion bioreactor system that enables a population of unselected human mononuclear bone marrow cells obtained from adult donors to expand up to 20 to 25-fold over a two-week period. Colony-forming units of granulocyte-macrophage (CFU-GM) progenitor cells expand 10 to 30-fold. These expansions depend on the gas phase oxygen concentration, the seeding density and time of cell harvest. Under operating conditions that allow for good cell proliferation, 3 to 4 million mononuclear cells can be obtained per square centimeter, with 0.5 to 0.8% being progenitor cells. Autologous human sera supported cell expansion as efficiently as animal sera. Increasing the size of the perfusion system to produce a clinically meaningful number of CFU-GMs could have important applications in bone marrow transplantation therapies.

Blood↗
PubMed1993

Tubed, folded radial forearm free flap for pharyngeal reconstruction and voice rehabilitation.

Reconstruction after total laryngectomy ideally includes restoration of voice with protected swallowing. Local flaps and tracheo-esophageal puncture with a prosthesis are widely used to accomplish this. Persistent problems, perhaps inherent to this solution, have led to the recent use of a tubed, folded radial forearm free flap for postlaryngectomy reconstruction. This flap has produced a good voice with low phonation pressures and minimal aspiration in 7 patients. A new configuration for this flap is described and 3 patients reported. Our flap's advantages include a simplified pedicle path, ease of construction, remote microanastomosis, and safer revision. Both patients with surviving flaps rapidly developed a good voice after reconstruction. Mild aspiration in 1 delayed oral intake and forced a successful revision. Our reconfigured flap may have some technical advantages, survives to length, and restores a good voice without significant aspiration. This and its simple care make it popular with patients. Development of this flap holds promise of more complete reconstruction after total laryngectomy.

Forearm↗