[Effect of cholesterol on the cooperativeness of the Ca-ATPase of the sarcoplasmic reticulum in rabbit skeletal muscle]. / Vliianie kholesterina na kooperativnost' Ca-ATFazy sarkoplazmaticheskogo retikulma skeletnykh myshts krolika.

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 3.2. It is assumed that increased cooperative interaction between Ca-ATPase polymers led to a rise in the efficacy of Ca-pump work. Under the conditions described the Nh for UTP increased from 0.43 to 1.0. During hypercholesterolemia (1 g/kg cholesterol for 1, 3 and 6 months), the maximal values of the Nh for ATP did not exceed 2.0, whereas those for UTP 1.0.

[Spin labels in the analysis of Ca-ATPase in the sarcoplasmic reticulum of rabbit skeletal muscles in hypercholesteremia]. / Issledovanie struktury Ca-ATFazy sarkoplazmaticheskogo retikuluma skeletnykh myshts krolika pri giperkholesterinemii metodom spinovykh metok.

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. It is concluded that the disordered function of the SR Ca-pump is a consequence of structural changes in the Ca-ATPase molecule in HC.

[Change in the molecular properties of sarcoplasmic reticulum Ca-ATPase during modification of the membranes with cholesterol]. / Izmenenie molekuliarnykh svoistv Ca-ATFazy sarkoplazmaticheskogo retikuluma pri modifikatsii membran kholesterinom.

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. It is inferred that the reduced efficacy of Ca-pump work found under the same experimental conditions before is a consequence of the modification of sarcoplasmic reticulum membranes with cholesterol and change in the molecular conformation of Ca-ATPase.

[Applicability of the integral form of the Michaelis-Menten equation for the kinetic study of transport ATPases]. / Primenimost' integral'noi formy uravneniia Mikhaélisa-Menten dlia kineticheskogo issledovaniia transportnykh ATF-az.

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. e. at 37 degrees, 26 degrees and 15 degrees C they are as follows: Km1--21, Km2--171; Km1--3.32, Km2--47; and Km1--1,2, Km2--20 microM, respectively. This method of determination of Km and V for transport ATPases compares favourably with the previously used methods in resulting efficiency.

[Effect of disseminated myocardial necrosis on ATPase activity, Ca2+ transport, and lipid peroxidation in cardiac mitochondrial and microsomal membranes]. / Vliianie rasseiannogo nekroza miokarda na ATF-aznuiu aktivnost', transport Ca2+ i perekisnoe okislenie lipidov membran mitokhondrii i mikrosom serdtsa.

Isoproterenol-induced (5 mg/kg) disseminated necrosis of the rabbit myocardium led to a decrease in the efficiency of calcium pump of sarcoplasmic reticulum fragments. This was shown by the reduced Ca/ATP ratio, as well as by Ca2+ and Ca2+ ATPase accumulation rate. In these conditions, calcium transport to mitochondria increased. Lipid peroxidation plays a definite role in the impairment of membrane permeability since the concentration of malonic dialdehyde rises in microsomal and mitochondrial fractions.U

[Calcium transport and ATPase activity of mitochondria and sarcoplasmic reticulum fragments of rabbit heart and muscle in hypercholesteremia]. / Transport kal'tsiia i ATF-aznaia aktivnost' mitokhondrii i fragmentov sarkoplazmaticheskogo retikuluma serdtsa i myshts krolikov pri giperkholesterinemii.

The rabbits were fed cholesterol diet (1 g/kg) for 3--7 months. As a result there was an increase in cholesterol concentration in mitochondrial membranes and fragments of sarcoplasmic reticulum (SPR) of the myocardium and skeletal muscles. Saturation of the membranes with cholesterol led to a decrease in the efficiency of SPR Ca-pump manifested by reduced Ca/ATP ratio and increased Ca2+ outflow rate from SPR. Under these conditions the rate of Ca2+ accumulation was higher in SPR than in the mitochondria. The activity of Mg2+, 2,4 DNF ATPase of the mitochondria declined in hypercholesterolemia.

[Several properties of the Ca-pump of rabbit skeletal muscle sarcoplasmic reticulum in hypercholesteremia]. / Nekotorye svoistva Ca-nasosa sarkoplazmaticheskogo retikuluma skeletnykh myshts krolikov pri giperkholesterinemii.

Sarcoplasmic reticulum (SR) fragments from the skeletal muscles of rabbit with marked atherosclerosis possessed decreased Ca2+-accumulating capacity. Lowering of transport efficiency, namely reduction of the Ca/ATP ratio from 1.9--normal value--to 0.9 during the experiment at 26 degrees C was accompanied by activation of Ca-ATPase and simultaneously of the rate of Ca2+ outflux from the SR. Arrhenius plots of Ca-ATPase temperature dependence characterized under normal conditions by a break at 20--21 degrees C was linearized under hypercholesterolemia. At the same time there was a rise (from 0.03 under normal conditions to 0.15 in atherosclerosis) of cholesterol/protein ratio in the SR membrane preparations. Activation energy for Ca-ATPase crude membranes under normal conditions was equal to 15.6 and 28.7 kcal/mol above and below the break point respectively; this value for Ca-ATPase of membranes with increased cholesterol level was 19 kcal/mol for all the temperatures investigated.