[Mechanism of nicotinic acid inhibition of the reaction catalyzed by acetyl-CoA carboxylase]. / O mekhanizme ingibirovaniia nikotinovoi kislotoi reaktsii, kataliziruemoi atsetil-CoA-karboksilazoi.

A kinetic analysis of the activity of acetyl-CoA carboxylase from chicken liver upon alimentary activation of lipogenesis and inhibition of this reaction by nicotinic acid was performed. It was found that the affinity of the enzyme isolated from chicken liver with stimulated lipogenesis is decreased by nicotinic acid for HCO3- but remains unchanged for ATP. The value of Vmax for ATP and the amount of the ATP used in this reaction remain unaffected. At the same time the enzyme affinity for acetyl-CoA is increased with a simultaneous decrease of Vmax. It is assumed that nicotinic acid inhibits the first step of the acetyl-CoA carboxylase-catalyzed reaction.

[Role of pyruvate dehydrogenase and ATP-citrate (pro-3S)lyase in inhibition of the biosynthesis of fatty acids by nicotinic acid]. / Rol' piruvatdegidrogenazy i ATP-tsitrat(pro-3S)liazy v ingivirovanii biosinteza zhirnykh kislot nikotinovoi kislotoi.

The pyruvate dehydrogenase and ATP-citrate(pro-3S)lyase activity in the liver after administration of nicotinic acid to chickens against a background of stimulated lypogenesis is shown to increase in the period of maximum fall of the acetyl-CoA-carboxylase activity. Affinity of ATP-citrate (pro-3S)-lyase to citrate at this time is lowered, the content of citrate and isocitrate is elevated and CoASac is decreased to some extent. A conclusion is made on the absence of substrate limitation of acetyl-CoA-carboxylase with administration of nicotinic acid to chickens under conditions of the fatty acid biosynthesis intensification.

[Effect of nicotinic acid on phosphodiesterase and adenyl cyclase activities in chicken liver]. / Vliianie nikotinovoi kisloty na fosfodiésteraznuiu i adenilattsiklaznuiu aktivnost' v pecheni tsypliat.

Stimulation of fatty acid biosynthesis by feeding high-carbohydrate diet to chickens after fasting induces a 38% and 23% rise in the 3':5'-cyclo-nucleotide phosphodiesterase and adenylate cyclase activities in the liver tissue, respectively. Administration of nicotinic acid (150 mg per 1 kg of weight) to chickens with stimulated biosynthesis of fatty acids leads to a sharp (70% at an average) decrease of 3':5'-cyclo-nucleotide phosphodiesterase activity, the adenylate cyclase activity under these conditions remains practically unchanged. The participation of the adenylate cyclase system in regulating the fatty acid biosynthesis under mentioned conditions, the role of phosphodiesterase are discussed.

[Effect of nicotinic acid on chicken liver protein kinase activity and cAMP content]. / Vliianie nikotinovoi kisloty na proteinkinaznuiu aktivnost' i soderzhanie cAMP v pecheni tsypliat.

The biosynthesis of fatty acids in the chicken liver was stimulated by feeding up chickens with high-carbon products. After fasting the cAMP content and protein kinase activity in chicken fall considerably as compared to the control. After administration of nicotinic acid to chicken under experiment the content of cAMP and the protein kinase activity in the liver tissue rise to the highest extent, returning to initial values by the end of the day. The maximal increase in the cAMP content and protein kinase activity coincides in time with the maximum of the acetyl-CoA-carboxylase activity decrease. An assumption is advanced that biosynthesis of fatty acids in the liver tissue of chickens is regulated by a change in the degree of acetyl-CoA-carboxylase phosphorylation with the participation of adenylate cyclase system.

[Nicotinic acid effect on acetyl-CoA-carboxylic activity in chicken liver]. / Vliianie nikotinovoi kisloty na atsetil-CoA-karboksilaznuiu aktivnost' tkani pecheni ts'shliat.

Changes of acetyl-CoA-carboxylase (EC 6.4.1.2) activity and the NAD content in the liver tissue were studied in dynamics after excessive administration of nicotinic acid to chickens. It is established that in chickens, which were given a high-carbohydrate diet after fasting, administration of nicotinic acid at first causes a fall of the acetyl-CoA-activity in the liver tissue, followed by its gradual rise against a background of the NAD content drop and by the 24th hour its level approaches the initial values. The maxima of NAD accumulation and of the acetyl-CoA-carboxylase activity decrease coincide in time. The administration of nicotinic acid to these chickens causes both a decrease in the intensity of 2-14C acetate incorporation into free fatty acids and a drop in their content.

[Inhibition of activity of acetyl-CoA-carboxylase from chicken liver by nicotinic acid and its derivatives]. / Ingibirovanie aktivnosti CoASAc-karboksilazy pecheni tsypliat nikotinovoi kislotoi i ee proizvodnymi.

Nicotinic acid and nicotinamide inhibit in vitro the acetyl-CoA-carboxylase activity of partially purified enzyme from chicken liver. The incorporation of 10, 20, 50 and 100 mkmoles of nicotinic acid or nicotinamide into the incubation medium (0,9 ml) leads to the inhibition of the enzyme activity by 19, 45, 70 and 100% and by 39, 51, 60 and 78%, respectively. NADH+ and NADP+ at concentrations by one order of magnitude lower than those of nicotinic acid and nicotinamide decrease the enzyme activity in a similar manner. The constants of inhibition by the above-mentioned compounds were calculated with respect to ATP, acetyl-CoA and citrate.

[Activity of NAD metabolism enzymes and DNA concentration in the liver during chicken ontogenesis]. / Aktyvnist' fermentiv obminu NAD ta vmist DNK u pechintsi kurchat v ontohenezi

A reverse interrelation is established between the content of NAD and DNA in the chickens liver at different stages of ontogenetic development, especially pronounced at the stages of embryogenesis. The content of NAD which is the least in the liver of the 8-day embryos increases with development of chickens and reaches the maximum level by the 6-month age. The content of DNA is maximum in the embryonal period. The activity of NAD-pyrophosphorylase in the liver nuclei has the low value at early periods of the embryonal life and rises with development of organism, reaching the constant values in one-, two- and 6-month chickens. Judging by the curve of the NAD-glycohydrolase activity in the liver nuclei, the hydrolase breakdown of NAD occurs only after chickens hatching.

[Properties of NAD-glycohydrolase of the nuclei of the liver cells of rats]. / Vlastyvosti NAD-hlikohidrolazi iader klityn pechinky shchuriv

Certain properties of the rat liver cell nuclei NAD-glycohydrolase (EC 3.2.2.5) were investigated. It is established that its highest activity is at 37 degrees with activation energy equal to 9480 cal/M and with factor Q10 equal to 1.5. The enzyme pH optimum in 0.2 M tris acetate is equal to 6.5 and in 0.2 potassium phosphate - 7.5. It was shown that the enzyme manifests its strict specificity only with beta-NAD, and it hardly decomposes NADP without affecting NADH, NADPH and NMN. The apparent Km value of the enzyme with respect to NAD is established. Isonicotinic acid hydrazide, nicotinamide and to the less extent nicotinic acid inhibit the enzymatic activity of nuclei. EDTA, EGTA, p-CMB, mercaptoethanol do not cause any changes in the rat liver cells nuclei NADase activity.