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Biomedical subjects

A D Keith

Publications and source records attributed to A D Keith.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1974

Viscosity of cellular protoplasm.

The protoplasmic viscosity was studied by using a small spin label having high permeability and broad solubility properties and nickel chloride as an extracellular spin-subtracting agent to localize signal inside cells. The viscosity is variable and in some cells is many times that of water or phospholipids, suggesting that lateral diffusion in biological membranes is important to cell function.

Chlamydomonas↗
PubMed1974

Spin label translational diffusion in solid tristearin.

Translational diffusion of the intermediate chain length spin label 7N14 has been detected and studied in a lipid environment which is in the bulk solid state. Under favorable circumstances this can occur at temperatures as much as 50 degrees C below the optical melting point. Translational diffusion allows 7N14 molecules to coalesce into impurity pools of high spin label concentration. Two other spin labels, 2N3 and 14N27, do not show a tendency to form such impurity pools. While 2N3 undergoes rapid tumbling at temperatures far below the melting point of the tristearin matrix, the molecules remain in an isolated state with no evidence of spin exchange. 14N27 is restricted in rotational motion in the solid matrix and also does not form impurity pools.

Animals↗
PubMed1972

Spin-label studies of dynamics of lipid alkyl chains in biological membranes: role of unsaturated sites.

Cultures of a yeast mutant, deficient in the synthesis of unsaturated fatty acids, were supplemented with either stearolic acid or with any one of three octadecanoic acids having a cis double bond 6, 9, or 11 carbons away from the acyl group. The resulting cells, with lipid alkyl chains well defined with respect to the position and nature of unsaturated sites, were then studied with spin-labeled stearic acids having a N-oxyloxazolidine ring located at 4, 6, 9, or 12 carbons away from the acyl group, and added in vitro to the cellular preparations. Differences in the molecular motion of each spin label were observed, as a function of the unsaturated site, in the intact yeast cells. Characteristic order to disorder phase transitions are inferred from data of temperature dependence. The results also indicate that triple bonds and cis double bonds inhibit a relatively ordered packing of lipid alkyl chains in the region between unsaturated sites and terminal methyl groups, leaving the hydrophobic region bounded by acyl groups and unsaturated sites unaffected.

Acylation↗