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Biomedical subjects

A D Keith

Publications and source records attributed to A D Keith.

16 recordsLinked to original sources
PubMed1977

Spin-label studies on the aqueous regions of phospholipid multilayers.

Water-soluble spin labels were used to study dimyristoyllecithin (DML) phospholipid multilayers. Previous studies report that there is a "bound" water region associated with dimyristoyllecithin containing about 10 molecules of water per phospholipid, a "trapped" water region located between the lamellae containing approximately 11 molecules per phospholipid, and a "ftion show that certain water-soluble spin-label mol-cules have their motional properties differentially modified by these three water environements. Furthermore, the labels also reveal the onset of lipid-phase transitions even though they have high water solubility. A phosphate-containing spin label demonstrated strong an isotropic motion in the lipid-water system above the phase transition but not below. The addition of cholesterol to the DML-water system removed the anisotropic motion of 2,2,6,6-tetramehtyl-4-phosphopiperidine-N-oxyl (Tempophosphate) and obscured the detection bound, trapped, and free water. In addition to the change-charge interactions between Tempophosphate and DML, two other spin labels were used both in the charged and uncharged states. 2,2,6,6-Tetramethyl-4-aminopiperidine-N-oxyl (Tempamine) in the charged state showed extremely strong anisotropic motion, presumably due to the interaction between the charged amine and the phosphate group of DML. When only partially charged, Tempamine showed much less anisotropic motion. PCA was analyzed at pH values where the carboxyl group was protonated and unprotonated. The resulting interaction was different at the two pH values. These water-soluble spin labels mimic ionic or nonionic solutes. Upon freezing, the spin labels are shown to be expelled from the ice regions into the remaining aqueous regions. The usefulness of this approach in studying solute behavior when freezing occurs and potential studies involving aqueous regions of cytoplasm are considered.

Binding Sites↗
PubMed1977

Factors restricting diffusion of water-soluble spin labels.

Line broadening of spin label signals is treated in terms of concentration, viscosity, charge and temperature dependencies. Line broadening of spin label signals may be caused either by spin label interactions or by the interaction between a spin label and a second paramagnetic species. Line broadening has been related to collision frequency in the literature and is treated in that way here. Collision frequency is related to diffusion processes in a way that allows information to be obtained about the diffusion environment. Several potential spin label line-broadening agents are compared as to their effectiveness. Small polymer beads with graduated pore sizes are used to show that collisional broadening has a marked dependence on the long-range structure of the diffusion environment. Application of these results to biological diffusion processes is considered.

Chemical Phenomena↗
PubMed1977

Inositol-less death in yeast results in a simultaneous increase in intracellular viscosity.

Inositol auxotrophs of yeast developing on isositol-deficient medium continue protein synthesis for 4-6 h, lose viability rapidly after 6 h, and show an increase in cytoplasmic viscosity as measured by spin label rotational motion. Cycloheximide prevents the rapid loss of cell viability, stops protein synthesis, and simultaneously prevents an increase in cytoplasmic viscosity. From these observations, we infer that intracellular translational diffusion is upset as a consequence of inositol starvation. Cell death may be caused by a modified intracellular diffusion environment.

Cell Survival↗
PubMed1977

Dynamic aspects of biological membranes.

Several aspects of membrane structure and function have been treated in which the dynamic properties of membrane components are particularly significant. The establishment and maintenance of asymmetries across the membrane, and heterogeneities in the plane of the membrane, place certain restrictions on the nature and extent of membrane fluid properties. Long-range order, which may give differential restrictions to rotational versus translational diffusion, requires specific interactions between membrane components that are strong enough to overcome thermal energy. Processes such as membrane fusion are likely to involve local areas in the membrane where certain membrane proteins are sequestered. And finally, the budding of virus membranes by mechanisms that specifically exclude host cell membrane proteins will require specialized interpretations in view of the fluid membrane model. These and other membrane phenomena illustrate the importance of the dynamic properties of membranes.

Animals↗
PubMed1976

Changes in the restriction of molecular rotational diffusion of water-soluble spin labels during fatty acid starvation of yeast.

Yeast mutants lacking fatty acid synthetase activity (fas-) die when deprived of saturated fatty acid under conditions which are otherwise growth-supporting. The spin label technique is used to show that restriction of molecular rotational diffusion of spin label molecules dissolved in aqueous zones increases several fold under conditions of fatty acid starvation while the apparent physical state of cellular hydrocarbon zones remains essentially unchanged. We focus attention on the cellular aqueous interior as the potential site of alteration under selective starvation conditions. Correspondences exist between restriction of molecular motion of water soluble spin labels dissolved in the cell and loss of cell viability. The correspondences to changes in the molecular motion of hydrocarbon soluble spin labels are much less or are not detectable.

Electron Spin Resonance Spectroscopy↗
PubMed1975

Spin label evidence for the role of lysoglycerophosphatides in cellular membranes of hibernating mammals.

The phospholipid composition of ground squirrel heart muscle changes during hibernation: more lysoglycerophosphatides are found in the hibernating state than in the active state. Phase transitions inferred from spin label motion occur in the usual manner typical of mammalian mitochondria for the mitochondria and mitochondrial lipids from active squirrels. However, a conspicuous absence of a spin label-detectable phase transition is observed in equivalent preparations from hibernating animals. The addition of lysolecithin to preparations from active squirrels removes the break and induces a straight line in the Arrhenius plot. The lack of a spin label-detectable phase transition in hibernating animals, therefore, is attributed to an increased content of lysoglycerophosphatides present in the phospholipids during hibernation.

Adaptation, Physiological↗
PubMed1975

Effect of isoniazid on the protoplasmic viscosity in Mycobacterium tuberculosis.

The effect of isoniazid on the protoplasmic viscosity in the H37Ra strain of Mycobacterium tuberculosis was determined by using electron spin resonance spectroscopy and a small spin label tempone (2,2,6,6-tetramethylpiperidone-N-oxyl radical). Isoniazid (0.5 mug/ml) caused the internal cellular viscosity to increase gradually over the first 15 h of exposure from a rotational correlation time value (T(c)) of 2.4 x 10(-10) to 3.4 x 10(10) s and then decrease linearly to the control level after 27 h. These results could be interpreted to mean that isoniazid allows a continued and normal synthesis of the protoplasmic components while the rate of increase in the cell volume is reduced. A degradative process may begin after the initial 15-h exposure time, which would cause the reduction in the internal viscosity.

Cytoplasm↗