The work is devoted to the study of the homocysteine concentration in blood plasma and the activity of the enzymes of cysteine catabolic transformations γ-glutamate-cysteine ligase and cysteine dioxygenase in rats’ hepatocytes under the conditions of consumption of excessive sucrose content on the background of alimentary protein deprivation. It was found, that the consumption of a high-sucrose diet in animals is accompanied by the increase of homocysteine concentration in plasma by 57% compared to control, whereas the excess of sucrose under the conditions of protein deficiency leads to hypohomocysteinemia (the content of homocysteine decreased by 43% compared to control). The increased plasma homocysteine levels in excess-consuming sucrose can be considered as a prognostic marker of functional disorders of the transsulfuration pathway in the liver and used in the diagnosis of hepatopathologies. Since, the cysteine content in liver cells increased under the conditions of high-sucrose diet consumption, the increasing γ-GCS, a key enzyme of glutathione synthesis, is probably associated with the maintenance of intercellular glutathione stores. Our data of the occurrence hypohomocysteinemia under the conditions of the consumption of excessive amounts of sucrose on the background of dietary protein deficiency highlight gaps in the understanding of the correlation between the metabolic processes of methionine, homocysteine and cysteine in the liver. Under the excessive consumption of sucrose on the background of protein deficiency, the exogenous protein deficiency can be considered as a key factor in reducing the γ-GCS activity (36%) and the cysteine content, because not only the amount of this amino acid is reduced but also its synthesis is disrupted. At the same time, the maximum increase in cysteine dioxygenase activity in rats’ hepatocytes under the conditions of high-sucrose/low-protein diet consumption on the background of decreased γ-GCS activity indicates the utilization of excess cysteine with the formation of taurine and sulfates.

This paper presents studies of nitric oxide and low-molecular S-nitrosothiols in the mitochondrial and cytosolic fractions of the rats' liver under the conditions of, alimentary protein deprivation, consumption of excess sucrose content and combined action of two adverse factors. In order to model the low-protein diet of the animal for 28 days received an isocaloric diet containing 4.7% protein, 10% fat, 81,3% carbohydrates (starch – 37%, sucrose – 30%, cellulose – 5%) and was calculated in accordance with the recommendations of the American Institute of Nutrition. The high-sugar diet consisted of 14% protein, 10% fat, 72% carbohydrates (starch – 37%, sucrose – 30%, cellulose – 5%). The mitochondrial and cytosolic fraction of rat liver cells were obtained by the method of differential centrifugation. Nitrogen oxide content was assessed by a unified method by determining the NO2- content, which is a stable metabolite of nitric oxide. Since NO is inactivated into an oxidase reaction with the conversion into nitrite or nitrate that is quickly metabolized, the nitrogen oxide content was assessed by the change in NO2-. The concentration of S-nitrosothiols was recorded, respectively, by determining the concentration of nitrite anion before and after the addition of Hg2+ ions, which by modifying the S – N bonds catalyzes the release of S-nitrosyl thiols of nitric oxide. An increase in NO content in both hepatic subcellular fractions of the rats’ experimental groups compared to control values was found. However, a lack of protein in the diet (protein deficiency in the diet leads to an increase in nitric oxide levels in 3-4 times) can be considered as a key factor in the recorded changes in the mitochondria of the animals’ liver, while in the cytosol - excessive consumption of sucrose (3-5 times increase). Regarding the level of S-nitrosothiols, in the studied fractions, multidirectional changes in their concentration were found. Thus, an increase in the content of nitrosyl derivatives in the mitochondria of rat’s liver cells with a simultaneous decrease in their level in the cytosol indicates dysmetabolic disorders in the transport system and deposition of nitric oxide, which can lead to the development of nitrosative stress under the experimental conditions.

The aim of the study was to investigate the activity of purine nucleotide catabolism enzymes, in particular, AMP-deaminase, 5'-nucleotidase, guanosine deaminase, and guanosine phosphorylase and xanthine oxidase in the cytosolic fraction of the liver of rats under conditions of different dietary supply of sucrose and dietary proteins. Enzyme activity was determined by photo colorimetric method: AMP-deaminase activity by the amount of ammonia formed by deamination of AMP, which has a maximum absorption at λ-540 nm and 5'-nucleotidase activity by the amount of Pn formed by hydrolysis of AMP at λ-8. The activity of guanosine phosphorylase, guanosine deaminase and xanthine oxidase was determined by spectrophotometric method. The results of studies have shown that due to consuming a high-sucrose diet in on the background of protein deficiency, the activation of purine nucleotide catabolism is observed and it can lead to disruption of the regulation of energy-dependent processes in liver cells. A critical factor influencing on the state of the purine nucleotide system and the activity of enzymes of their catabolism is alimentary protein deficiency.

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