Yu. A. Treschenkova - Senior Research Scientist, N.M. Emanuel Institute of Biochemical Physics, Russian Academy of Science, Moscow, Russia. E-mail: tresch@sky.chph.ras.ru

It is now know that alpha-tocopherol (AT) involved in various physiological functions in the cell is not associated with antioxidant activity [1]. For example, the AT may modulate the activity of some enzymes as post-translational level, and at the level of transcription and, with its lipophilic properties affect the membrane structure. Previously, we have shown that chronic gamma- irradiation in small dose (0,6 rad/d) affects the isoenzymes composition of lactate dehydrogenase (LDH) in cytoplasm of mice brain cells. Also revealed different sensitivity of LDH in subcellular fractions of brain (cytoplasm, microsomes and mitochondria) to small and large doses of AT [2]. In this study was investigated of the effects of low doses of gamma-irradiation (16 rad/min), the doses of AT in 10-14 mol/kg (SMD) or 10-4 mol/kg, and their combined effect on the kinetic properties (Vmax/mg protein, Km, Vmax/Km) of the LDH of mice brain synaptosomes. Mice once were irradiated for 1 min. Different doses of AT was administered 40 min before irradiation. The brain was removed the day after the affect of irradiation or AT+irradiation. Brain synaptosomes were obtained by differential centrifugation and purified by a sucrose gradient. LDH activity was determined spectrophoto-metrically at 340 nm with substrates pyruvate or lactate in a wide range of concentrations. LDH catalyzes the reaction pyruvate+ NADH ↔ lactate+ NAD+. It is shown that only irradiation increases Vmax/mg protein with the substrate pyruvate of LDH and reduces it with the substrate lactate compared to the control (fig. 1). Efficiency (Vmax/Km) of LDH decreases mainly for lactate. AT in both doses increases Vmax/mg protein and Vmax/Km with the two substrates LDH. Vmax/mg protein with the substrate pyruvate remaines high, while Vmax/mg protein with lactate substantially reduces compared to the control by action of the combined effect AT+ irradiation. Irradiation or AT+ irradiation are significantly shift the reaction towards the formation of lactate and NAD+, which are important metabolites for physiological cell function.