Biochemical compartmentation of gluconeogenic enzymes in fish tissues

Compartmentation of liver, kidney muscle and gill tissues in relation to glucose-6-phosphatase and fructose 1,6-diphosphatase was examined in the fishes Labeo rohita, Clarias batrachus and Channa punctatus. The anterior region of the right and left lobes of the liver contained the maximum of fructose 1,6-diphosphatase and glucose-6-phosphatase, while the minimum was in the right and left lobes of gill tissue. Herbivore fish had the highest gluconeogenic enzyme content followed by carnivore and piscivore species. The observed enzymatic variations in the three fish species were discussed.     

Biochemical compartmentation of fish tissues VII non-specific phosphomonoesterases in vital organs

The viscera were compartmentalised in relation to non-specific phosphomonoesterase in a major carp, a catfish and a murrel. Activity was highest in the middle region of the kidney and lowest in the cephalic region of muscle. The observed variations in various regions of the viscera are discussed in relation to feeding habits, growth rate and biochemical make-up of the viscera.     

Biochemical compartmentation of fish tissues: chronic toxicity of mercuric nitrate on visceral phosphomonoesterases in Channa punctatus (Bloch)

Effect of sub-lethal dose of mercuric nitrate was studied in anterior, middle and posterior regions of kidney, anterior and posterior regions of left and right liver lobes, cephalic, thoracic and caudal regions of muscle and left and right gill tissues of C. punctatus in relation to acid and alkaline phosphatase under chronic studies. Middle region of kidney registered maximum rise and fall of acid and alkaline phosphatase, respectively. Right lobe of liver showed more rise and fall of acid and alkaline phosphatase activity respectively. Similarly, left gill is more pronounced than the right one. The observed enzymatic variations were discussed in relation to the biochemical constituents and physiological coordination rendered by these tissues.     

The compartmentation of glycolytic and gluconeogenic enzymes in rat kidney and liver and its significance to renal and hepatic metabolism

Summary An indirect immunoperoxidase procedure has been used to demonstrate sites of glycolysis and gluconeogenesis in normal rat kidney and liver. In kidney, the gluconeogenic enzyme fructose 1,6-biphosphatase was restricted to the proximal tubular epithelium, while the glycolytic enzyme hexokinase predominated in more distal segments. Intense staining for the biphosphatase in proximal convoluted tubular brush borders suggests that reabsorbed substrates may be used directly at this site in renal gluconeogenesis. In view of the high phosphofructokinase and pyruvate kinase activities present in collecting ducts, their relatively low hexokinase activities and their relatively pale immunostaining for hexokinase indicate that glycolytic substrates which feed into the pathway subsequent to the initial phosphorylation step, rather than glucose, may be the major energy source for the rat renal papilla.Immunostaining in the liver was consistent with the metabolic zonation of liver parenchyma, in that glucokinase occurred mainly in perivenous regions and fructose 1,6-bisphosphatase in periportal areas. The presence of such metabolic zonation is difficult to reconcile with the widely held view that the majority of hepatic glucogen is derived directly from glucose. A model for hepatic glycogen synthesis is proposed which links the concept of parenchymal zonal heterogeneity with recent biochemical evidence concerning the glucose paradox and with microscopical studies on the dynamics of glycogen deposition after refeeding.     

Rutin improves glucose homeostasis in streptozotocin diabetic tissues by altering glycolytic and gluconeogenic enzymes

The role of rutin on carbohydrate metabolism in normal and streptozotocin (STZ)-induced diabetic rats was investigated in the present study. Administration of STZ led to a significant (p <0.05) increase in fasting plasma glucose and a decrease in insulin levels. The content of glycogen significantly (p <0.05) decreased in liver and muscle, but increased in kidney. The activity of hexokinase decreased whereas the activities of glucose-6-phosphatase and fructose-1,6-bisphosphatase significantly (p <0.05) increased in the tissues. Oral administration of rutin (100 mg/kg) to diabetic rats for a period of 45 days resulted in significant (p <0.05) alterations in the parameters studied but not in normal rats. A decrease of plasma glucose and increase in insulin levels were observed along with the restoration of glycogen content and the activities of carbohydrate metabolic enzymes in rutin-treated diabetic rats. The histopathological study of the pancreas revealed the protective role of rutin. There was an expansion of the islets and decreased fatty infiltrate of the islets in rutin-treated diabetic rats. In normal rats treated with rutin, we could not observe any significant change in all the parameters studied. Combined, these results show that rutin plays a positive role in carbohydrate metabolism and antioxidant status in diabetic rats.     

Inactivation of gluconeogenic enzymes in glycolytic mutants of Saccharomyces cerevisiae.

Yeast mutants blocked at different steps of the glycolytic pathways have been used to study the inactivation of several gluconeogenic enzymes upon addition of sugars. While phosphorylation of the sugars appears a requisite for the inactivation of fructose 1,6-bisphosphatase and phosphoenol-pyruvate carboxykinase, malate dehydrogenase is inactivated by fructose in mutants lacking hexokinase. The normal inactivation elicited by glucose in a mutant lacking phosphofructokinase indicates that the process does not require metabolism of the sugar beyond hexose monophosphates. A possible role for ATP in the inactivation process is suggested.     

Circadian changes of gluconeogenic enzymes in irradiated rats

The authors studied the effect of whole body irradiation at different times of day on the circadian rhythms of gluconeogenic enzymes. They found that: 1. liver and kidney enzyme activities were highest in the light part of the day and lowest in the middle of the dark part; 2. 12-h circadian rhythm of glucose-6-phosphatase and fructose-1, 6-bisphosphatase activity in the liver and the renal cortex followed a similar course; 3. a lethal whole body dose of 14.4 Gy X-rays did not affect the circadian oscillation curves of the given enzymes, with the exception of fructose-1, 6-bisphosphatase in the liver of irradiated rats, where the rhythm was lost.     

A selective system for hepatoma cells producing gluconeogenic enzymes.

Gluconeogenesis is a liver-specific pathway which permits the synthesis of phosphorylated sugars from oxaloacetate, pyruvate, amino acids, or trioses. The absolute requirement for glucose or an alternative hexose which characterizes most mammalian cells probably reflects an inablility to perform gluconeogenesis rather than to generate sufficient energy by respiration alone. Cells of diverse histogenetic origins have been tested in glucose-free medium, supplemented with oxaloacetate or with dihydroxyacetone. The only cells able to grow are well-differentiated hepatoma cells which produce the relevant gluconeogenic enzymes: phosphoenolpyruvate carboxykinase, fructose diphosphatase, and triokinase. Reconstruction experiments demonstrate that glucose-free media permit the selective growth of cells producing gluconeogenic enzymes. These media should be useful for analysis of reexpression of differentiated functions in somatic cell hybrids and for the isolation of mutants.     

Distribution of FMRFamide-like immunoreactivity in the brain of the elasmobranch fish Scyliorhinus canicula.

The distribution of FMRFamide-like-immunoreactive peptides was investigated in the brain and pituitary of the elasmobranch fish Scyliorhinus canicula using the indirect immunofluorescence technique. FMRFamide-immunoreactive cells and fibers were mainly observed in the telencephalon and the diencephalon, while other brain structures were almost unstained. In the telencephalon, FMRFamide-like-containing neurons were seen in the caudal part of the area periventricularis pallialis, in the posterior area of the nucleus septi medialis and in the nucleus septi caudoventralis. In the diencephalon, numerous FMRFamide-positive cell bodies were observed in the hypothalamus, ventral thalamus and posterior tuberculum. The highest density of immunofluorescent perikarya was found in the nucleus lobi lateralis hypothalami and in the nucleus periventricularis hypothalami. More caudally, the mesencephalon and the caudal brainstem only contained scattered varicose FMRFamide-immunoreactive fibers. Stained fibers were also identified in the median eminence and several FMRFamide-like-positive cells were detected in the dorsal and rostral parts of the neurointermediate lobe of the pituitary. These data indicate that substances related to the molluscan cardioexcitatory peptide FMRFamide are widely distributed in the brain of S. canicula, suggesting their implication in neuroendocrine and/or neuromodulatory functions.     

Distribution and function of digestive tract chitinolytic enzymes in fish

The activity of chitinolytic enzymes in the stomach or foregut of 29 North European marine and freshwater fish were determined. No correlation with a chitin-eating feeding habit was observed but species that were able to mechanically disrupt prey had low activity while species that ingest prey whole had high activity. The primary function of gastric chitinase in fish may be to chemically disrupt the chitinous envelope of prey.     

Evaluation of key gluconeogenic enzymes in experimental biliary obstruction

In order to evaluate the usefulness of key gluconeogenic enzymes, in relation to the markers commonly used (alkaline phosphatase and gamma-glutamyl transpeptidase) for the diagnose of cholestasis the serum activity of phosphoenolpyruvate carboxykinase, fructose 1,6-bisphosphatase and glucose-6-phosphatase has been measured in rats with bile-duct ligation. Among the gluconeogenic enzymes studied only phosphoenolpyruvate carboxykinase activity increased significantly in the first 48 hours after cholestasis, decreasing thereafter to normal values. Both alkaline phosphatase and gamma-glutamyl transpeptidase activities showed a very significant increase which persisted throughout the experiment. These results seem to indicate that in spite of the high organ specificity of these enzymes they do not appear to be useful for the diagnosis of cholestasis.     

Serum activity of the key gluconeogenic enzymes in carbon-tetrachloride-induced experimental hepatotoxicity

Serum activity has been measured in three of the key enzymes in the gluconeogenic pathway in rats subjected to experimental hepatotoxicity after intraperitoneal administration of carbon tetrachloride. The levels of phosphoenolpyruvate carboxykinase (PEPCK) and fructose-1,6-biphosphatase (FBPase) showed a similar behavior to the transaminase (AST and ALT), increasing markedly with respect to the controls at 12 h after administration of the poison, reaching their maximum peak of activity at between 24 and 36 h, and returning to normal values at 96 h. The activity of glucose-6-phosphatase was not significantly modified throughout the treatment. These results seem to demonstrate that the determination of the serum activity of PEPCK and FBPase could be a sensitive and specific marker of hepatic cytolysis.