James M. Lyons

The influence of membranes on the temperature-induced changes in the kinetics of some respiratory enzymes of mitochondria.

Abstract Disruption and fragmentation of mitochondria from rat liver and sweet potato tissue by sonication, hypotonic swelling, and freezing and thawing is shown to have little or no effect on the discontinuity in the Arrhenius plot exhibited by the mitochondrial respiratory enzymes of these tissues. After disruption of the mitochondrial membranes with detergent, however, the succinate oxidase system, succinate dehydrogenase and cytochrome c oxidase of both tissues each exhibits a uniform activation energy over the temperature range of 1 to 36 °. The results suggest that the temperature-induced change in activation energy of the membrane-bound enzymes is associated with a phase change in the lipid component of the membranes which induces a configurational change in the enzyme proteins.

A temperature-induced transition in mitochondrial oxidation: Contrasts between cold and warm-blooded animals

Abstract 1. 1. Arrhenius plots for succinate oxidation by mitochondria from homeothermic animals indicate a phase change at approximately 23°C with an increased activation energy below this transition temperature. 2. 2. Similar plots for poikilotherms are continuous and linear with no change in activation energy over the entire range from 4–30°C. 3. 3. These results are suggested to be related to a direct response to temperature causing a configurational change of the membrane associated enzyme proteins induced by a phase change in the membrane lipids in homeotherms not observed in poikilotherms.

Temperature “breaks” in Arrhenius plots: A thermodynamic consequence of a phase change

Abstract Temperature “breaks” in Arrhenius plots of biological data are real and can be explained as a consequence of a phase change in the system.

Solidification of unsaturated/saturated fatty acid mixtures and its relationship to chilling sensitivity in plants

Freezing points of mixtures of palmitic and linoleic, or palmitic and linolenic acids, the predominant fatty acids in plants, decrease slowly as the unsaturated fatty acid is increased to 60 mole %. Beyond this per cent the freezing point is depressed quite markedly by each addition of unsaturated fatty acid. Linoleic and linolenic acids have similar effects on the freezing points of the mixtures until about 82 mole % unsaturated fatty acid. Differences of less than 5% in the amount of unsaturated fatty acid have a marked effect on the freezing point of mixtures at the approximate composition of fatty acid in plant membrane lipids.

[23] Polarographic determination of phase changes in mitochondrial membranes in response to temperature

Publisher Summary Phase transitions in biological membranes have been determined by a variety of techniques and assays; including X-ray diffraction, differential calorimetry, z enzymatic activity, and electron spin resonance spectroscopy with spin labels. Polarographic measurement of mitochondrial oxidation has also been used successfully to indirectly determine the appearance of membrane phase changes in response to temperature. This method is based on the observation that the respiratory enzymes of mitochondria undergo a change in conformation at the same temperature at which the associated membranes undergo a phase transition. The material presented indicates the particular techniques and problems associated with polarographic assay at different temperatures.

Utilization of model membranes in a test for the mechanism of ethylene action

SummaryReversible alteration of the surface tension of thin films of lipids, proteins and mixtures of both resulted when the thin films were treated with ethylene and other aliphatic gases. This effect appeared to be a nonspecific surface effect related to the molecular size of the gases. Ethylene produced no change which would ascribe to it any specific properties in this test system. The conductivity of an egg lecithin-cholesterol bilayer membrane separating two electrolytes was unaffected by all the test gases (including ethylene), but chloroform vapors markedly altered the conductivity in a reversible manner. In each of the test systems empoloyed, there was no specificity exhibited by ethylene, either qualitatively or quantitatively, indicating the mechanism of ethylene action cannot be explained as a simple physical effect on membranes.

The induction of energized configurational changes in plant mitochondria,in vivo

Configurational changes in the mitochondrial membranes of the salt gland ofTamarix aphylla, which are dependent on the biochemical state of the mitochondria, are demonstrated. In the energized state the cristae expand and become closely associated. There is also an increase in the density of the matrix and a formation of strands of material in the matrix and between the closely associated cristae membranes. The energized condition can be discharged by incubation in a medium containing 2,4-dinitrophenol and the mitochondria are comparable to those observed in glands fixed by typical methods for electron microscopy.

Characterization of fatty acids from root and shoot lipids ofCapsicum species

Lipids were extracted from the roots and shoots of four species of theCapsicum (pepper) genus and separated into three fractions: triglycerides; free fatty acids, mono- and diglycerides; and phospholipids. The component fatty acids were determined by subjecting the methyl esters to gasliquid chromatography. The predominate fatty acids obtained were palmitic (16∶0) and linoleic (18∶2), with lesser amounts of linolenic (18∶3), stearic (18∶1), and oleic (18∶0). Differences existed in the neutral lipid fractions which might be of value from taxonomic interests; however, the phospholipids from each of the species and plant parts did not differ so greatly. A comparison of the amount of unsaturated fatty acids in the phospholipid fractions indicates that differences exist which might be of value in determining the relative sensitivity of the several species to chilling temperatures.