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Biomedical subjects

A Keith

Publications and source records attributed to A Keith.

34 records · Page 2Linked to original sources
PubMed1974

Electron spinal resonance analysis of the nitroxide spin label 2,2,6,6-tetramethylpipidone-N-oxyl (Tempone) in single crystals of the reduced Tempone matrix.

The nitroxide spin label Tempone (2,2,6,6-tetramethylpiperidone-N-oxyl) can be reduced with ascorbic acid to give a nonparamagnetic species. Single crystals of reduced Tempone serve as a suitable host matrix to orient trace quantities of Tempone for ESR analysis. In these crystals the majority of the Tempone molecules are well-oriented, but a smaller fraction of the molecules tumble freely to give an isotropic electron spin resonance (ESR) spectrum. ESR transitions for the oriented molecules are saturated at much lower microwave power levels than for the tumbling molecules. For the oriented molecules, an analysis of the anisotropy of the spectroscopic splitting factor (g) gives principal values of g(1) = 2.0094, g(2) = 2.0061, g(3) = 2.0021. The hyperfine coupling tensor is nearly axially symmetric, with principal values (in gauss) of A(1) = 6.5, A(2) = 6.7, A(3) = 33.0. Within experimental error, the principal axis systems for the g tensor and the hyperfine tensor are identical. Comparison of the average values of g and A with the isotropic values of these parameters for Tempone in solvents of different polarity suggests a method for choosing the most appropriate tensor elements to be used for spin label experiments in various solvent systems.

Crystallization↗
PubMed1974

Active transport of choline by a marine pseudomonad.

A marine pseudomonad, BAL-31, accumulates the phospholipid nitrogen base, choline, although no detectable amount of choline is incorporated into polar lipids. Metabolic inhibitors such as cyanide and azide block the uptake process as does starving for oxygen by using nitrogen gas. Only very close structural analogues show any inhibition of transport, indicating that the uptake process has great structural specificity. The export of choline out of the cells is also an energy-dependent process and is markedly reduced during oxygen depletion. The constitutive level of choline transport is increased by approximately a factor of three after a brief induction period. Two other gram-negative bacteria also accumulate choline, whereas a gram-positive bacterium, Bacillus subtilis, and a yeast, Saccharomyces cerevisiae, fail to show any detectable accumulation.

Acetylcholine↗
PubMed1973

Spin label motion in fatty acids.

Spin labels dissolved in highly purified fatty acid systems exhibit nearly identical tumbling rates in liquid and solid phases. Even though the spin labels do not have the same molecular geometry as the lipid matrix the melting point of the matrix can be inferred by measurements of the temperature dependency of molecular motion.

Chromatography, Thin Layer↗
PubMed1970

Spin-labeled Neurospora mitochondria.

Spin-label studies were carried out on Neurospora mitochondria under in vivo and in vitro labeling conditions. A long-chained spin-labeled fatty acid was incorporated by Neurospora and was found in mitochondrial phospholipids. The molecular motion at various temperatures was different from that for the same spin label under in vitro labeling conditions. The results for spin-labeled mitochondria were compared with those from isolated lipids and with those from aggregates of spin-labeled fatty acid and isolated bovine serum albumin. These comparisons suggest that the hydrocarbon portions of membranes are relatively fluid and are not extensively restricted in motion by association with proteins.

Cell Membrane↗
PubMed1970

Membrane structure: spin labeling and freeze etching of Mycoplasma laidawii.

A spin-labeled fatty acid was incorporated in vivo into the polar lipids of Mycoplasma laidlawii membranes. The electron paramagnetic resonance signal from either intact cells or their extracted lipids reflected the fatty acid composition of the Mycoplasma membranes. Comparison of signals from intact cells, gramicidin-treated cells, heat-treated cells, and extracted lipids indicates that a major portion of the membrane lipids is in a semiviscous hydrocarbon environment. The results also show that the spin label in the intact membrane is slightly but significantly less mobile than it is in protein-free lipid extracts made from these membranes. Correlated electron microscope examinations using the freeze-etch technique reveal particulate components in the hydrophobic region of the membrane. The mobility of the lipids in the intact cell membrane may be influenced by their association with these particles.

Cell Membrane↗