The activity and kinetic parameters of endoplasmic reticulum Ca<^>2+, Mg<^>2+-ATPase (SERCA) of blood lymphocytes in patients with ovarian cancer (OC) have been examined. It is known that cancer cells usually have the disturbance of calcium homeostasis. Although the changes of Ca<^>2+-signaling can not be considered as a prerequisite for the initiation of cancer, the consequences of the changes of the structure and functioning of Ca<^>2+-channels or other Ca<^>2+-transporting systems in cancer cells can be significant in the tumor progression. SERCA is an intracellular Ca<^>2+-store and a multifunctional organelle that performs a variety of Ca<^>2+-dependent functions involved in the homeostatic and signaling mechanisms. Plasma membrane Ca<^>2+, Mg<^>2+-ATPase and endoplasmic reticulum Ca<^>2+, Mg<^>2+-ATPase are two Ca<^>2+-transporting structures which regulate Ca<^>2+-concentration in cytosol. It is assumed that the endoplasmic reticulum Ca<^>2+, Mg<^>2+-ATPase in the lymphocytes plays a leading role in the process of reducing the Ca<^>2+ level in cytosol. It has been found that SERCA activity of blood lymphocytes in the almost healthy individuals has been (2,25 +- 0,17) mu mol Pi/min per 1 mg of protein. According to the stats, the SERCA activity of blood lymphocytes in the patients with OC has been significantly different from the control group. Its value has been decreased by 1,5 times (p << 0,001), compared to the almost healthy subjects. The decrease of the plasma membrane Ca<^>2+, Mg<^>2+-ATPase activity that has been demonstrated earlier and in SERCA activity of blood lymphocytes in the patients with OC, indicates the increase of [Ca<^>2+]i in cytosol of lymphocytes. Both Ca<^>2+, Mg<^>2+-ATPase and Na<^>+, K<^>+-ATPase use the energy of ATP hydrolysis to carry ions against their electrochemical gradient. Therefore, the changed concentration of ATP in the incubation medium may affect the rate of ATP-hydrolysis reaction. The dependence of Ca<^>2+, Mg<^>2+-ATPase activity on the substrate concentration (ATP) in the incubation medium has been determined by the value of the affinity constant of the substrate (KATP). It has been calculated by determining the Ca<^>2+, Mg<^>2+-ATPase activity in the incubation medium containing the substrate in the concentration ranging from 0,1 to 5,0 mM (with a constant concentration of Ca<^>2+ - 0,05 mM and Mg<^>2+ - 5 mM). It has been found that the increase of ATP concentration in the incubation medium in the concentration ranging from 0,1 to 4,0 mM has led to the gradual monotonic increase of SERCA activity of lymphocytes in the almost healthy subjects. The maximum ATP-hydrolase activities of SERCA of blood lymphocytes in the healthy donors and patients with OC have been noticed when ATP concentration in the incubation medium has been 4 mM. Researching of the concentration dependence of Ca<^>2+, Mg<^>2+-ATPase activity on ATP concentration shows that throughout the range of the substrate concentrations, the SERCA activity in the patients with OC has been decreased compared to the control group.

• Воробець Дмитро Зіновійович (медичні науки)
• Онуфрович Олена Костянтинівна (біологічні науки)
• Воробець Зіновій Дмитрович (фармацевтичні науки)

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