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Biomedical subjects

O H Griffith

Publications and source records attributed to O H Griffith.

122 records · Page 7Linked to original sources
PubMed1969

Orientation of lipid spin labels in lecithin multilayers.

Nitroxide-labeled stearic acid and cholestane have been incorporated into lecithin multilayers. The pronounced anisotropy of the preparations reflects a nonrandom structure of the lecithin film and demonstrates that these lipid probes can report structural information from lipid regions resembling those thought to occur in membranes. These two probes differ with respect to the orientation of the NO bond to the long axis, but both orient with their long axes perpendicular to the phospholipid film. Simulated spectra, calculated on the basis of a Gaussian distribution of orientations, are in agreement with the experimental results.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

Photoelectron microscopy and photoelectron quantum yields of the fluorescent dyes fluorescein and rhodamine.

Photoelectric properties of the dyes fluorescein and rhodamine were determined with the aim of assessing the usefulness of these compounds as labels in photoelectron microscopy. The photoelectron quantum yields were measured over the wavelength range 180-230 nm. At 230 nm the quantum yields for fluorescein disodium salt, rhodamine B free base and rhodamine B HCl salt are approximately 10(-5) electrons per incident photon. At 180 nm these values rise to approximately 10(-3) electrons per incident photon. All forms of fluorescein do not have the same quantum yield. The neutral form of fluorescein has a quantum yield an order of magnitude lower than the disodium salt. Beam current measurements were performed on labeled and unlabeled proteins to determine the effect of the high light intensity employed in the photoelectron microscope. The initial beam current measurements and the quantum yield curves are consistent and demonstrate that there is significant contrast between labeled and unlabeled proteins. However, after several minutes in the photoelectron microscope, the proteins become more photoemissive and the contrast diminishes. This change in contrast explains several puzzling observations in the literature.

Electrons↗
PubMedDate not supplied

Photoelectron microscopy of erythrocyte ghosts: imaging of lectin binding sites with colloidal gold markers.

Images of human red cell ghosts have been obtained by photoelectron microscopy (photoemission electron microscopy or PEM) without any staining, metal coating or shadowing. Membrane folding, when it occurs in these collapsed structures, shows up clearly even though the membrane itself is only 5-10 nm in thickness. Using red cell ghosts as a model system, it is shown that colloidal gold can act as a photoemissive marker. Specific lectin binding sites on the cell surface were labeled with a colloidal gold-wheat germ agglutinin complex. The gold particles were readily detectable against the weaker emission from the cell surface.

Colloids↗
PubMedDate not supplied

Synthesis of fluorogenic substrates for continuous assay of phosphatidylinositol-specific phospholipase C.

An improved synthesis of fluorogenic substrate analogues for phosphatidylinositol-specific phospholipase C (PI-PLC) is described. The water-soluble substrates, which are derived from fluorescein, are not fluorescent until cleaved by the enzyme, and provide a convenient means to continuously monitor PI-PLC activity. The improvement in the synthesis lies in the method used to protect the hydroxyl groups of the inositol portion of the substrate molecule and allows a milder deprotection procedure to be used. The result is a much more reproducible synthesis of the substrate. The improved procedure has been employed to synthesize a series of fluorogenic substrates, which differ in the length of the aliphatic tail attached to the fluorescein portion of the molecule. The length of the tail was found to have a significant effect on the rate of cleavage of these substrates.

Fluorescein↗