Information about the catalytic and kinetic properties of mitochondria NO-synthase from uterus smooth muscle is missing currently. According to the data on MitoTracker Orange CM-H2TMRos and 4-аmino-5-methylamino-2',7'-difluorescein, diaminofluorescein-FM (DAF-FM) dye co-localization in uterine smooth muscle cells, presented in this paper, NO can be synthesized in their mitochondria. High activity of NO synthase requires the presence of substrates of respiration, L-arginine, Ca 2+ and NADPH. It is established that the dependence of NO production on the concentration of L-arginine has a bell-shaped character with a maximum of 75 μM, and the apparent affinity constant for L-arginine is 28.9 ± 9.1 μM. The dependence of NO production on Ca 2+ concentration has a maximum at 100-250 μM; the activation constant for Ca 2+ is 44.4 ± 14.5 μM. The inhibitor of Ca 2+ transport in mitochondria ruthenium red (RuR), as well as the inhibitor of NO-synthase N G -nitro-L-arginine (NA), reduces NO production. The biosynthesis of NO by mitochondria depends on its energized level: it is stimulated by the addition of respiration substrates, suppressed with specific inhibitors of the electron transport chain (rotenone and antimycin A) and carbonyl-cyanide 3-chlorophenylhydrazone (CCCP) protonophore.

It was proved that No synthesis in isolated mitochondria of rat uterus smooth muscle depended on the entry of exogenous ca 2+ to mitochondria (inhibited by 1-10 mM Mg 2+ in the absence of ATP and by 10 μM ruthenium red) and was suppressed by calmodulin antagonists (0.1-10 μM calmidazolium and 1-100 μM trifluoperazine). It was blocked by N G -nitro-l-arginine, a known antagonist of the constitutive No-synthase, with a half-maximal inhibition effect at about 25 μM. Moderate deholesterinization of the plasma membrane of myocytes after processing with 0.01% digitonin was followed by increased nitric oxide biosynthesis by cells. The data obtained suggested that mitochondria and plasmalemma is a possible source of No synthesis in uterine myocytes. k e y w o r d s: nitric oxide, mtNoS, mitochondria, calcium, uterus smooth muscle.

Modern data on biochemical patterns of nitric oxide biosynthesis in mammal cells from l-arginine in normoxic conditions is described. The attention of the authors is given to the results of the recent years on the structure and regulation features isoforms of No-synthase. The emphasis is put on the latest conception of the compartmentalization of certain isoforms of these enzymes in cells and on the possibility of the directed transport of nitric oxide in the vascular wall. The central place in the review is devoted to issues on the endogenous formation of NO in mitochondria and its potential physiological significance. Our own results on the identification of NO in mitochondria of the uterine smooth muscle, biochemical characteristics of this process and NO possible role in Са 2+ transport regulation by organelles are presented and discussed. K e y w o r d s: nitric oxide, mitochondria, No-synthases, cell compartments, calcium, smooth muscle. I n foreign scientific literature and, partly, in national periodicals, there are numerous review papers devoted to various aspects of the formation and biological activity of nitric oxide and its derivatives (nitric active forms). In view of this, in the presented article the authors tried to provide general ideas about the biosynthesis regularities and the role of NO in a cell in the most summarized version, primarily focusing on the problems that have become relevant in the last period of research, such as compartmentalization of certain isoforms of NO-synthase in cells and the possibility of directed transport of nitric oxide in the vascular wall. Particular attention is paid to the less highlighted and investigated problem -mitochondria own synthesis of nitric oxide and its possible functional activity in this compartment. Available material relates only to the synthesis of NO from L-arginine in the presence of O 2 and does not include important issues on reductase activity in hypoxic conditions and the functioning of the nitric oxide cycle in the mammalian organism. Numerous works by prof. Reutov V. P. and, for example, a review article in Ukrainian are devoted to these problems [1].Nitric oxide (NO) is a structurally simple low molecular amphiphilic free radical molecule. In biosystems NO has a relatively short time of existence (up to 5 sec depending on microenvironment) and can migrate at short distances from the generation sites what is determined by the rate of oxidation [2]. This limitation of diffusion implies the specificity of NO effect in individual cell compartments due to the colocalization of target proteins with NO sources in a multiprotein complex of signalosomes.Synthesis of NO in a cell is provided by the family of isoforms of NO-synthase (NOS), which, with the participation of NADPH as an electron source and the presence of O 2 , carry out a five-electron two-stage oxidation of the L-arginine guanidine group with the formation of NO and L-citrulline [2][3][4][5][6][7].NO is an almost universal messenger and regulatory molecule. NO signaling is carrie...