[Effect of cholesterol on the cooperativeness of the Ca-ATPase of the sarcoplasmic reticulum in rabbit skeletal muscle].

Cooperative properties of Ca-ATPase of the sarcoplasmic reticulum (SR) of rabbit skeletal muscles were examined in health and hypercholesterolemia. As the concentration of ATP was raised (from 50-100 microM to 5 mM) the Hill ratio (Nh) for ATP increased from 0.4 to 3.

[Spin labels in the analysis of Ca-ATPase in the sarcoplasmic reticulum of rabbit skeletal muscles in hypercholesteremia].

The method of electron paramagnetic resonance with spin-labeled maleimide was used to study variation of the structure of Ca-ATPase of the sarcoplasmic reticulum (SR) in rabbit skeletal muscles under long-term hypercholesterolemia (HC). The rate of the maleimide spin label binding with Ca-ATPase of the SR was decreased in HC, which correlated with a lesser access of spin-labeled thiol groups for potassium ferricyanide and sodium ascorbate. HC led to a considerable reduction in the lability and to enhancement of hydrophobia of the spin-labeled fragment of the enzyme.

[Change in the molecular properties of sarcoplasmic reticulum Ca-ATPase during modification of the membranes with cholesterol].

The thiol reagent NBD-chloride (4-chloro-7-nitro-benzo-2-oxo-1,3-diazole) was used to determine the amount and reactivity of SH-groups of Ca-ATPase of rat skeletal muscle sarcoplasmic reticulum during hypercholesterolemia. Modification of membranes with cholesterol brought about a decrease in the total amount and reactivity of SH-groups at the cost of reduction of rapid SH-groups and decrease of the modification constant of these SH-groups. The masking effect of high concentrations of ATP on the reactivity of SH-groups in hypercholesterolemia was noticed.

[Applicability of the integral form of the Michaelis-Menten equation for the kinetic study of transport ATPases].

Applicability of the integrated form of the Michaelis-Menten equation to kinetic analysis of transport ATPases has been shown during continuous pH-metric recording of their activity. Two values of Km for both Na, K-ATPase and Ca-ATPase have been found to be consistent with the reported data. Both values of Km for Na, K-ATPase change with temperature, i.