1.The earlier observation that aging promotes peroxidation of lipids within inner mitochondrial membranes by a radical-generating mechanism has provided a model for studying the relationship of membrane alterations to energy-linked respiration.2. Electron transport was impaired as a function of age only in the presence of substrates oxidized within the inner mitochondrial membrane. Respiratory control ratios and P : 0 ratios decreased regardless of substrate identity.3. Arrhenius kinetic data revealed age-dependent shifts of temperature breaks only for membranebound enzymes including oligomycin-sensitive ATPase. Specific activities decreased for all enzymes studied except cytochrome oxidase and the glutamate oxidase system. 4. Molecular motion data of spin-labelled fatty acid analogues associated with phospholipid bilayer from inner mitochondrial membranes exhibited a decrease in lipid fluidity in membranes from aged rats.5. The exposure of isolated mitochondria to a 0; -radical generating system brought about identical changes in energy-linked respiration and oxidative phosphorylation as did aging in the animal. The effect was completely inhibited only in the presence of both superoxide dismutase and catalase, indicating the participation of 0 2 -radicals and H202 in causing the observed structural and functional changes.6. The results support the concept of an active mechanism in mitochondria of living tissues which can contribute to pathophysiological processes by a sequential reaction involving radicalinduced changes in the hydrophobic bonding of lipid-dependent enzyme systems.
Leucocidin from Pseudomonas aeruginosa (strain 158) induced loss of potassium from isolated hepatocytes. The (Na+-K+) stimulated ATPase activity of isolated rat liver plasma membranes showed dose-dependent activation up to 56%. Electron-spin-resonance (ESR) measurements gave no indication of toxin-induced changes in membrane fluidity. On isolated guinea pig heart auricles the toxin produced an increase in frequency from 180/min to about 300/min, with arrhythmia and transitory flutter. On isolated nerve-diaphragm preparations the toxin caused a contracture and a decline in twitch tension, with a loss of potassium into the bathing solution. The action potential of the electrically stimulated N. ischiadicus of rat or frog was not affected when leucocidin was added to the bathing solution up to a concentration of 10 micrograms/ml.
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