[Interrelationship between structural and functional modifications in the membranes of the sarcoplasmic reticulum...

Structural and functional modifications of sarcoplasmic reticulum membranes from skeletal muscles by molecular oxygen was studied. Lipid peroxidation (accumulation of 5-10 nmoles hydroperoxides/mg lipids) results in membrane permeability increase for Ca2+-ions whereas the activity of Ca2+-dependant ATPase preserved unchanged. In the temperature range 5-30 degrees C decrease of solubilization parameter alpha (for nitroxide radical 2,2,6,6-tetramethylpiperidin-1-oxyl) was registered while alpha reached the control values at temperatures higher than 30 degrees C. Further increase in lipoperoxide content (more than 20 nmoles/mg lipids) lead to inhibition of Ca2+dependant ATPase. In this case alpha was lower than in intack membranes in the whole temperature interval investigated. The loss of Ca2+-accumulating capacity is explained on the basis of peroxide clusters formation in lipid bilayer regions of sarcoplasmic membrane. One of the mechanisms of Ca2+-dependant ATPase inhibition after lipid peroxidation is the deficiency of polyunsaturated fatty acyls in microenvironment of the enzyme.