[Mechanism of tocopherol stabilization of sarcoplasmic reticulum Ca2+-ATPase from thermodenaturation activated by fatty acids].

The stabilizing effect of alpha-tocopherol on the enzymatic system of Ca2+ transport in sarcoplasmic reticulum (SR) membranes of rabbit skeletal muscle was studied. Exogenous fatty acids (e. g. arachidonic) cause destabilization of the enzymatic Ca2+ transport system by decreasing the thermal stability of Ca2+-dependent ATPase and the Ca2+-transport ability (Ca/ATP ratio) of SR membranes. Incorporation of alpha-tocopherol into SR membranes increases the thermal stability of the enzymatic Ca2+ transport system exposed to the damaging action of free fatty acids. Using differential scanning microcalorimetry, it was shown that arachidonic acid causes a shift of the maximum on the curve for the temperature dependence of specific thermal capacity of SR membranes towards the low temperature region. Under a combined action of arachidonic acid and alpha-tocopherol the position of the maxima on the temperature dependence curve for specific thermal capacity of SR membranes is close to the control value. A quantitative estimation of the values of molar enthalpies for SR membrane thermodenaturation demonstrated that the melting of Ca2+-dependent ATPase, the main intrinsic protein of SR membranes, is biphasic. The data obtained are discussed in terms of hypothetical mechanisms of protection of the enzymatic Ca2+ transport system against the damaging action of free fatty acids.