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Biomedical subjects

J K Raison

Publications and source records attributed to J K Raison.

At least 37 records · Page 2Linked to original sources
PubMed1978

Changes in lipid ordering and state of aggregation in lymphocyte plasma membranes after exposure to mitogens.

An electron spin probe study was made of the effect of a number of mitogenic agents on the ordering and state of aggregation of the plasma membrane lipids of lymphocytes. These agents, which included phytohemagglutinin, Concanavalin A, the calcium ionophore A23187 and periodate, caused a 20% decrease in lipid ordering in the region of the bilayer probed by 5-nitroxide stearic acid. The corresponding methyl ester probe showed marked probe-probe interaction under the same conditions indicating an aggregation of lipids in the area probed by this label. Studies with mixed lipid vesicles and ganglioside-free cells indicate that these areas are rich in glycolipids capable of hydrogen bonding to the ester probe. The decrease in ordering and the increase in aggregation of the membrane lipids were correlated with the patching and capping of the ligand-receptor complexes. Furthermore, the disappearance of fluorescent ligand from the surface of treated cells corresponded with the return of the spectral parameters of the probes to control cell values. It was concluded that glycolipids might play an important role in ligand-induced cell surface changes either as bearers of receptor groups, as in the case of some gangliosides, or in association by hydrogen-bonding with receptor proteins.

Animals↗
PubMed1977

Wheat mitochondria: oxidative activity and membrane lipid structure as a function of temperature.

Mitochondrial oxidative activity and membrane lipid structure of two wheat (Triticum aestivum L.) cultivars were measured as a function of temperature. The Arrhenius activation energy for the oxidation of both succinate and alpha-ketoglutarate was constant over the temperature range of 3 to 27 C. The activation energy for succinate-cytochrome c oxidoreductase activity was also constant over the same temperature range. The concentration of mitochondria in the reaction, the degree of initial inhibition of state 3 respiration, and the time after isolation of mitochondria were each shown to be capable of causing a disproportionate decrease in the rate of oxidation at low temperatures which resulted in an apparent increase in the activation energy of oxidative activity. Using three spin-labeling techniques, wheat membrane lipids were shown to undergo phase changes at about 0 C and 30 C. It is concluded that the membrane lipids of wheat, a chillingresistant plant, undergo a phase transition similar to the transition observed in the membrane lipids of chilling-sensitive plants. For wheat, however, the transition is initiated at a lower temperature and extends over a wider temperature range.

Journal Article↗
PubMed1976

The response of plant mitochondria to media of high solute content.

The state-3 rate of respiration of potato tuber mitochondria is inhibited by concentrations of KCl or NaCl above 125 mM, and by concentrations of sucrose, lactose, or maltose above 500 mM, but not at all by mannitol, glucose, glycine, or proline up to a concentration of 1500 mM in the medium. Mitochondria from cauliflower, beetroot, cucumber, rock melon, and watermelon behave very similarly to those from potato tuber. The variable response to different solutes proves that the reduction in respiration is not a simple function of the chemical potential of water in the medium. Disruption of potato mitochondria by ultrasonic vibration does not relieve the inhibition of succinate oxidation caused by KCl or sucrose. However, treatment with detergent abolishes completely the inhibition of respiration by sucrose. Inhibition of succinate dehydrogenase [Succinate:PMS, oxidoreductase (EC.1.3.99.1)] and malate dehydrogenase [L-Malate:NAD oxidoreductase (EC.1.1.1.37)] activities by sucrose is less than the inhibition of succinate- and malate-dependent oxygen uptake by the potato mitochondria. Limited substrate uptake and, alternatively, reduced electron flow as a consequence of a direct effect of solute on the mitochondrial membrane are considered as possible mechanisms of inhibition.

Amino Acids↗
PubMed1973

Occurrence of a Temperature-induced Phase Transition in Mitochondria Isolated from Apple Fruit.

Mitochondria were isolated from fruit of six cultivars of apples differing in susceptibility to the physiological disorder, low temperature breakdown. The state 3 rate of succinate-dependent oxygen uptake and the motion of a spin label were measured at from 0 to 25 C. Arrhenius plots of the data showed that the apparent energy of activation of both respiration and motion of the spin label increased abruptly at low temperatures indicative of a temperature-induced phase change in the membrane lipids. The changes were detected with mitochondria from all of the cultivars, but the temperature at which the changes occurred did not correlate with the susceptibility of the cultivars to low temperature breakdown.

Journal Article↗