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Biomedical subjects

M W Davidson

Publications and source records attributed to M W Davidson.

At least 19 recordsLinked to original sources
PubMed1995

Clinicians' attitudes toward no-suicide agreements.

Though no-suicide agreements are widely used and often recommended for suicidal patients, their sparse empirical support leads to questions regarding their use with patients of various ages. To answer this question, 46 licensed psychologist members of a Southern state psychology association answered questions regarding their beliefs and attitudes about no-suicide agreements. Such agreements were considered more appropriate for adults or adolescents than children. They were judged highly appropriate with moderately suicidal patients and were expected to help patients postpone suicide until after a crisis had past and to help reduce clinicians' anxiety.

Adolescent↗
PubMed1990

Resonance Raman investigation of a soluble cytochrome c552 from alkaliphilic Bacillus firmus RAB.

The environment of the heme site of a low-potential soluble cytochrome (c552) from alkaliphilic Bacillus firmus RAB has been characterized with resonance Raman scattering and compared to that of horse heart cytochrome c. The Raman data indicate that vibrational bands sensitive to the axial ligation of the heme, as well as modes sensitive to the heme peripheral environment in cytochrome c552, are distinct from those of horse heart cytochrome c. The spectra of cytochrome c552 display resonance Raman modes indicative of a methionine as the sixth ligand in the oxidized form, while the reduced form appears to contain a nitrogenous-based sixth ligand. In addition, Q-band excitation reveals differences among vibrational modes in cytochrome c552 that are sensitive to the amino acid environment surrounding the heme.

Animals↗
PubMed1989

Electron microscopy of liquid crystalline DNA: direct evidence for cholesteric-like organization of DNA in dinoflagellate chromosomes.

Freeze-fracture-etch replicas of concentrated DNA solutions which appeared, by polarized light microscopy, to be in a cholesteric-like liquid crystalline state were examined by high resolution transmission electron microscopy (TEM). Individual DNA molecules were resolvable, and the microscopic morphologies observed for such replicas confirmed the cholesteric organization of DNA molecules in this liquid crystalline state. Furthermore, replica morphologies were strikingly similar to TEM images of dinoflagellate chromosomes in both thin section and freeze-etch replicas, providing strong support for the cholesteric DNA packing model proposed for the organization of DNA in these chromosomes by Bouligand and Livolant.

Animals↗
PubMed1988

Purification and characterization of two soluble cytochromes from the alkalophile Bacillus firmus RAB.

A soluble cytochrome c and soluble cytochrome b were purified from the alkalophilic Bacillus firmus RAB. The cytochrome c, with an alpha band at 552 nm, had an apparent molecular weight of 16,500 and was acidic, with a pI of 3.4. At both pH 7.0 and 8.3, the midpoint potential of c-552 was +66 mV. Above pH 8.3, the cytochrome exhibited a pH-dependent decrease in midpoint potential. This property, among others, distinguished the cytochrome c-552 from other membrane-associated c-type cytochromes. The soluble cytochrome b, with an alpha band maximum at 558 nm, had a molecular weight of approx. 15,500 and was also an acidic protein, with a pI of 3.07. It exhibited a pH-independent midpoint potential of +28 mV.

Amino Acids↗
PubMed1988

Spectroscopic and ligand-binding properties of an oxygen-binding heme protein from Chromatium vinosum.

Magnetic circular dichroism spectra were obtained for the oxidized and reduced forms of cyanide, azide and carbon monoxide complexes of an O2-binding hemeprotein isolated from the photosynthetic purple sulfur bacterium, Chronatium vinosum. Cyanide binding to the protein, which results in formation of a low-spin complex, was highly pH dependent with little complex formation observed at pH values near or below 7.

Azides↗
PubMed1988

Multiple liquid crystal phases of DNA at high concentrations.

DNA packaging in vivo is very tight, with volume concentrations approaching 70% w/v in sperm heads, virus capsids and bacterial nucleoids. The packaging mechanisms adopted may be related to the natural tendency of semi-rigid polymers to form liquid crystalline phases in concentrated solutions. We find that DNA forms at least three distinct liquid crystalline phases at concentrations comparable to those in vivo, with phase transitions occurring over relatively narrow ranges of DNA concentration. A weakly birefringent, dynamic, 'precholesteric' mesophase with microscopic textures intermediate between those of a nematic and a true cholesteric phase forms at the lowest concentrations required for phase separation. At slightly higher DNA concentrations, a second mesophase forms which is a strongly birefringent, well-ordered cholesteric phase with a concentration-dependent pitch varying from 2 to 10 micron. At the highest DNA concentrations, a phase forms which is two-dimensionally ordered and resembles smectic phases of thermotropic liquid crystals observed with small molecules.

Crystallization↗
PubMed1987

Spectroscopic and kinetic properties of an oxygen-binding heme protein from Chromatium vinosum.

Resonance Raman and electron paramagnetic resonance spectroscopy have been utilized to identify histidine as an axial heme ligand in a high spin, heme c-containing protein isolated from the photosynthetic purple sulfur bacterium Chromatium vinosum. Resonance Raman spectroscopy has also been used to characterize the CO adduct of the C. vinosum hemoprotein. Resonance Raman spectra of the heme site obtained within 10 ns of CO photolysis from the ferrous hemoprotein are virtually identical to those of the unligated protein, indicating that there is little or no rearrangement of the heme pocket in response to ligand photolysis. The equilibrium constant for CO binding to the ferrous hemeprotein was measured to be 1.7 X 10(-5) M-1 and the CO association rate constant determined to be 5.4 X 10(3) M-1 S-1. The quantum efficiency for photodissociation of the hemoprotein X CO complex was greater than or equal to 0.9.

Carbon Monoxide↗
PubMed1986

Complex formation and electron transfer between mitochondrial cytochrome c and flavocytochrome c552 from Chromatium vinosum.

Flavocytochrome c552 from Chromatium vinosum catalyzes the oxidation of sulfide to sulfur using a soluble c-type cytochrome as an electron acceptor. Mitochondrial cytochrome c forms a stable complex with flavocytochrome c552 and may function as an alternative electron acceptor in vitro. The recognition site for flavocytochrome c552 on equine cytochrome c has been deduced by differential chemical modification of cytochrome c in the presence and absence of flavocytochrome c552 and by kinetic analysis of the sulfide:cytochrome c oxidoreductase activity of m-trifluoromethylphenylcarbamoyl-lysine derivatives of cytochrome c. As with mitochondrial redox partners, interaction occurs around the exposed heme edge at the "front face" of cytochrome c. However, the domain recognized by flavocytochrome c552 seems to extend to the right of the heme edge, whereas the site of interaction with mitochondrial cytochrome c oxidase and reductase is more to the left. Km but not Vmax of the electron transfer reaction with mitochondrial cytochrome c increases with increasing ionic strength. The correlation of chemical modification and ionic strength dependence data indicates that the electrostatic interaction between the two hemoproteins involves fewer ionic bonds than that with other redox partners of cytochrome c.

Acetylation↗
PubMed1979

Comparative viscometric analysis of the interaction of chloroquine and quinacrine with superhelical and sonicated DNA.

Unwinding angles for the structurally related antimalarial drugs chloroquine and quinacrine have been determined with superhelical Col E1 plasmid DNA by applying the quantitative method developed by Vinograd and co-workers (Revet, B.M., Schmir, M. and Vinograd, J. (1971) Nat. New Biol. 229, 10). The value for chloroquine, 8.6 degrees, calculated assuming an unwinding angle of 26 degrees for ethidium bromide, is significantly lower than the value for quinacrine, 22.5 degrees, calculated in the same manner. Viscometric titrations with sonicated calf thymus DNA were quantitated using available binding constants for the two drugs and indicated that chloroquine also causes significantly smaller DNA length increases on intercalation relative to quinacrine. The conclusion from these experiments is that chloroquine does not bind to DNA by the classical intercalation mechanism typical of quinacrine and ethidium.

Bacteriocin Plasmids↗
PubMed1978

Synthesis of as-triazines as potential antiviral agents.

Four acenaphtho[1,2-e]-as-triazines and 11 5,6-diaryl-as-triazines, all substituted with an aliphatic or aromatic amino function in the 3-position, were synthesized. Two acenaphthotriazines were active against vesicular stomatitis virus in tissue culture.

Animals↗
PubMed1977

The interaction of propidium diiodide with self-complementary dinucleoside monophosphates.

The interactions of a quinacrine derivative, methylated at both the aromatic and aliphatic nitrogens, and propidium diiodide with the dinucleoside monophosphates CpG, GpC, UpA and ApU have been investigated using 13C-NMR (for the quinacrine derivative prepared with [13C]methyl substituents and 1H-NMR and ultraviolet-visible spectroscopy. The quinacrine derivative displayed negligible interaction with the dinucleosides at concentrations up to 5 - 10(-4) M. Propidium did form complexes with dinucleosides even at concentrations as low as 10(-4) M. Propidium displayed a pyrimidine-purine binding preference and gave especially large changes in ultraviolet-visible and 1H-NMR spectra in the presence of CpG. This suggests that propidium forms an intercalated complex with a Watson-Crick hydrogen-bonded CpG dimer. At higher concentrations UpA and GpC gave similar spectral changes indicating that they could also form significant amounts of an intercalated complex with propidium under appropriate conditions. The changes caused by ApU were small under all conditions and were more similar to the effects caused by mononucleotides. These results indicate that, at least for phenanthridines, cationic side chains do not greatly inhibit complex formation with dinucleoside monophosphates, and suggest that the weak interaction of the quinacrine derivative with dinucleosides is due to weaker interactions of the acridine ring system with nucleoside bases relative to the phenanthridine ring system.

Chemical Phenomena↗