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Biomedical subjects

S M Newman

Publications and source records attributed to S M Newman.

At least 37 records · Page 2Linked to original sources
PubMed1991

A nuclear mutant of Chlamydomonas that exhibits increased sensitivity to UV irradiation, reduced recombination of nuclear genes, and altered transmission of chloroplast genes.

Meiotic progeny of Chlamydomonas reinhardtii normally receive chloroplast genomes only from the mt+ parent. However, exceptional zygotes, which transmit the chloroplast genomes of both parents or, more rarely, only those of the mt- parent, arise at a low frequency. Mutations at the mt(+)-linked mat-3 locus were found previously to elevate the transmission of chloroplast genomes from the mt- parent, resulting in a much higher than normal frequency of exceptional zygotes. In this paper we demonstrate that an ultraviolet-sensitive nuclear mutation mapping at the uvsE1 locus, which is unlinked to mating type, also promotes chloroplast genome transmission from the mt- parent. This mutant, which was previously shown to reduce recombination of nuclear genes in meiosis, acts synergistically with the mat-3-3 mutation to produce an extremely high frequency of exceptional zygotes. Through the use of restriction fragment length polymorphisms existing in the chloroplast genomes of C. reinhardtii and the interfertile strain C. smithii, we show that chloroplast DNA fragments from the mt- parent normally begin to disappear shortly after zygote formation. However, this process appears to be blocked totally in the absence of wild-type uvsE1 and mat-3 gene products. Our findings are consistent with the hypothesis that both gene products contribute to the mechanism responsible for uniparental inheritance of the chloroplast genome from the mt+ parent.

Alleles↗
PubMed1991

Chorionic structure of the egg of the screwworm, Cochliomyia hominivorax (Diptera: Calliphoridae).

The chorion of the Cochliomyia hominivorax (Coquerel) egg is described using observations from scanning and transmission electron microscopy and light microscopy. Included are the gross structure and surface characteristics of the chorion, the basic architecture and internal components of the chorion proper, the location and function of the hatch lines, and the functional morphology of the plastron region as a respiratory structure. In the regular hexagonal arrangement and form of individual structural units, the chorion of the screwworm egg exhibits basic architectural features common to other higher Diptera. Within the open spaces of the endochorionic layer, however, are previously undescribed membranous structures of unknown function which appear to line the cavities of the endochorion. The plastron region partially encircles the micropyle (anterior end) of the egg and extends along the dorsal surface to the posterior pole; it is delineated laterally by the hatch lines. The chorion ruptures along the anterior region of the hatch lines as the larva emerges. The plastron region is composed of elaborate stalked aeropyles above a highly dissected inner reticulum. This structure is believed to function as a respiratory organ when the egg is immersed in fluid.

Animals↗
PubMed1991

Amalgam alternatives: what can compete?

I have not discussed the full veneer restoration of metals or ceramics. These are costly services-between four and six times amalgam's cost. No clinical evidence supports longevity much greater than amalgam. Full veneer restoration requires significant reduction of tooth structure and may also require a buildup for appropriate retention. A buildup requirement again debates the question of alternative to amalgam. Full cast restorations have not been discussed as legitimate alternatives, though partial veneers would be equivalent to onlay procedures. Full veneer procedures are better suited to significant reconstructions of tooth structure, and only then when there can be some expectation of home care by the patient. Dr. Miles Markley extolled the use of amalgam during his career. He was innovative in creating extremely conservative preparations, and the placement procedures for quality amalgam restorations. He stated: "Amalgam is the standard." All techniques for single tooth restoration, whether esthetic or not, could stand a comparison to this standard. There are materials and techniques that begin to compare well with amalgam. No one material or technique fits all the needs amalgam has fulfilled, but some can begin to compete.

Composite Resins↗
PubMed1990

Transformation of chloroplast ribosomal RNA genes in Chlamydomonas: molecular and genetic characterization of integration events.

Transformation of chloroplast ribosomal RNA (rRNA) genes in Chlamydomonas has been achieved by the biolistic process using cloned chloroplast DNA fragments carrying mutations that confer antibiotic resistance. The sites of exchange employed during the integration of the donor DNA into the recipient genome have been localized using a combination of antibiotic resistance mutations in the 16S and 23S rRNA genes and restriction fragment length polymorphisms that flank these genes. Complete or nearly complete replacement of a region of the chloroplast genome in the recipient cell by the corresponding sequence from the donor plasmid was the most common integration event. Exchange events between the homologous donor and recipient sequences occurred preferentially near the vector:insert junctions. Insertion of the donor rRNA genes and flanking sequences into one inverted repeat of the recipient genome was followed by intramolecular copy correction so that both copies of the inverted repeat acquired identical sequences. Increased frequencies of rRNA gene transformants were achieved by reducing the copy number of the chloroplast genome in the recipient cells and by decreasing the heterology between donor and recipient DNA sequences flanking the selectable markers. In addition to producing bona fide chloroplast rRNA transformants, the biolistic process induced mutants resistant to low levels of streptomycin, typical of nuclear mutations in Chlamydomonas.

Chlamydomonas↗
PubMed1989

Analysis of Chromophytic and Rhodophytic Ribulose-1,5-Bisphosphate Carboxylase Indicates Extensive Structural and Functional Similarities among Evolutionarily Diverse Algae.

Ribulose-1,5-bisphosphate carboxylase (Rubisco) from the algae Olisthodiscus luteus (chromophyte) and Griffithsia pacifica (rhodophyte) are remarkably similar to each other. However, both enzymes differ significantly in the structure and function when compared to Rubisco from green algae and land plants. Analysis of purified Rubisco from O. luteus and G. pacifica indicates that the size of the holoenzyme and stoichiometry of the 55 and 15 kilodalton subunit polypeptides are approximately 550 kilodaltons and eight:eight for both algae. Antigenic determinants are highly conserved between the O. luteus and G. pacifica enzymes and differ from those of the spinach subunit polypeptides. Sequence similarity between the two algal large subunits has been further confirmed by one-dimensional peptide mapping. Substrate ribulose bisphosphate has no effect on the rate of CO(2)/Mg(2+) activation of O. luteus and G. pacifica enzymes which contrasts to the extensive inhibition of spinach Rubisco activation at similar concentrations of this compound. In addition, the Michaelis constant for CO(2) and the inhibition constant for 6-phosphogluconate are similar for the O. luteus and G. pacifica catalyzed carboxylation reaction. Both values are intermediate to those observed for the tight binding spinach enzyme and weak binding prokaryotic (Rhodospirillum rubrum) enzyme. The biochemical similarities documented between O. luteus and G. pacifica may be due to a common evolutionary origin on the chromophytic and rhodophytic chloroplast but could also result from the fact that both subunit polypeptides are chloroplast DNA encoded in these algal taxa.

Journal Article↗
PubMed1988

Nitinol arch wire in a simulated oral environment: changes in mechanical properties.

Changes in the mechanical properties of a nickel-titanium orthodontic alloy, nitinol (0.016-inch arch wires), were studied in a simulated oral environment across time, at various levels of acidity, and at different amounts of static deflection. Significant decreases in specific mechanical properties were observed in these incubated wires compared with a group kept dry and unstressed. Ultimate tensile strain, modulus of elasticity, and 0.2% yield strength each decreased. Acidity (pH 3 to 7) and amount of deflection (0 to 4 mm in a 10-mm span) did not affect the wire, but there was a significant, monotonic decrease in yield strength with time in the simulated oral environment. By 4 months this measure of susceptibility to permanent deformation increased by 15%. Consequently, long-term use (or reuse) of a nitinol wire may be associated with a modest, but statistically significant, degradation in performance, notably in the limit of the wire's elasticity.

Alloys↗
PubMed1988

The corrosion resistance of a new cobalt-chromium-molybdenum-ceramic alloy.

Cobalt-chromium alloys are extensively used for removable partial dentures and implants. Recently, this type of alloy has been introduced for porcelain-fused-to-metal crown and bridgework. The objective of this in vitro study was to evaluate the corrosion behaviour of such a ceramic alloy (Vicomp) and compare it to a cobalt-chromium alloy for removable partial dentures (Vitallium). A 0.9% saline solution and an artificial saliva were used as electrolytes. Results indicate a similar, adequate, corrosion resistance.

Ceramics↗
PubMed1987

Structural, Functional, and Evolutionary Analysis of Ribulose-1,5-Bisphosphate Carboxylase from the Chromophytic Alga Olisthodiscus luteus.

Ribulose-1,5-bisphosphate carboxylase (RuBPCase) was purified from the marine chromophyte Olisthodiscus luteus. This study represents the first extensive analysis of RuBPCase from a chromophytic plant species as well as from an organism where both subunits of the enzyme are encoded on the chloroplast genome. The size of the purified holoenzyme (17.9 Svedberg units, 588 kilodaltons) was determined by sedimentation analysis and the size of the subunits (55 kilodaltons, 15 kilodaltons) ascertained by analytical sodium dodecyl sulfate gel electrophoresis. This data predicts either an 8:9 or 8:8 ratio of the large to small subunits in the holoenzyme. Amino acid analyses demonstrate that the O. luteus RuBPCase large subunit is highly conserved and the small subunit much less so when compared with the chlorophytic plant peptides. The catalytic optima of pH and Mg(2+) have been determined as well as the response of enzyme catalysis to temperature. The requirements of NaHCO(3) and Mg(2+) for enzyme activation have also been analyzed. The Michaelis constants for the substrates of the carboxylation reaction (CO(2) and ribulose bisphosphate) were shown to be 45 and 48 micromolar, respectively. Competitive inhibition by oxygen of RuBPCase-catalyzed CO(2) fixation was also demonstrated. These data demonstrate that a high degree of RuBPCase conservation occurs among widely divergent photoautotrophs regardless of small subunit coding site.

Journal Article↗
PubMed1986

The relationship of metals to the general health of the patient, the dentist and office staff.

Recently a few dental practitioners have asserted that some of the metallic dental restorative materials can be toxic to patients. In particular, nickel from base-metal casting alloys and mercury from silver amalgam have been implicated. Nickel is a strong allergen and a weak carcinogen. However, current evidence does not support the view that the making and use of base-metal cast restorations causes an increased incidence of either of these problems in dental personnel or in patients. Mercury rarely causes allergy but the possibility of such an event must be remembered. Mercury has a strong potential for causing chronic toxicity. Dental personnel must use caution in the handling of free mercury in the process of making amalgam restorations. There is evidence that mercury can be released from dental amalgam restorations, but only in very small quantities. Except for the claims of those practitioners who decry the use of dental amalgam, there is no evidence to support the view that there is a toxic hazard to patients who have amalgam restorations.

Adult↗
PubMed1984

Direct bonding of orthodontic brackets to esthetic restorative materials using a silane.

Along with adult orthodontics comes a concern for direct-bonding techniques with esthetic anterior restorative materials. Two such materials available today are porcelain and a heat-cured composite resin. The ability to bond orthodontic brackets to these materials was tested with a normal direct-bonding technique. In addition, silane was used to theoretically enhance the bond to porcelain and the glass component of the composite. A normal acid-etch procedure to enamel served as a comparison. Bonding equivalent to the enamel acid-etch procedure was achieved with the heat-cured composite, whether silane was used or not. Silane enhanced the bond to porcelain, but the bond might not be adequate for clinical effectiveness.

Acid Etching, Dental↗
PubMed1983

Thiosemicarbazide-induced osteolathyrism in metamorphosing Xenopus laevis.

Exposure of Xenopus laevis tadpoles to thiosemicarbazide (TSC), at concentrations from 10 to 75 mg/liter, causes an inhibition of metamorphosis and produces the classic manifestations of the experimental disease, osteolathyrism. Concentration-dependent effects of TSC exposure are observed in growth rate and in the severity of the osteolathyrogenic effect. Concentrations allowing the most rapid growth produce the more extreme osteolathyrogenic defects. Osteolathyrism in these animals is identical in characteristics to the condition described in a wide variety of vertebrate species. In Xenopus, osteolathyrism is expressed morphologically as anomalies in bone development, skeletal conformation, and abnormal connective tissue organization in the aorta wall. The underlying defect responsible for these observations is apparently a perturbation of collagen fiber formation and maturation, as evidenced ultrastructurally by aberrant distribution and packing of collagen fibers. It is suspected that TSC produces this effect by altering the availability of copper ion, a cofactor to lysyl oxidase, an essential enzyme for intermolecular cross-linking of procollagen. This step in collagen metabolism has been consistently implicated as the site of action of several osteolathyrogenic agents. Xenopus tadpoles present a classic response to this known osteolathyrogen and demonstrate a high degree of uniformity of response within the experimental groups. In view of the developmentally significant events accessible with this system and inherent logistic and economical advantages, the metamorphosing tadpole of Xenopus holds considerable potential for the experimental analysis of teratogenic agents and events.

Animals↗