Kidney gluconeogenesis

Nearly All Gluconeogenesis Occurs In the Liver and Kidneys in Animals... 

U (No CaM) < O Q. CL Heart, kidney, Brain, liver, widespread Cardiac function, Ca2+-dependent regulation, hormonal regulation of gluconeogenesis, cell proliferation, coincidence detector for NO... 

Succinyl-CoA is converted to succinate by the enzyme succinate thiokinase (succinyl-CoA synthetase). This is the only example in the citric acid cycle of substrate-level phosphorylation. Tissues in which glu-coneogenesis occurs (the hver and kidney) contain two isoenzymes of succinate thiokinase, one specific for GDP and the other for ADP. The GTP formed is used for the decarboxylation of oxaloacetate to phos-phoenolpymvate in gluconeogenesis and provides a regulatory hnk between citric acid cycle activity and the withdrawal of oxaloacetate for gluconeogenesis. Nongluconeogenic tissues have only the isoenzyme that uses ADP. 

The pathway of gluconeogenesis in the liver and kidney utilizes those reactions in glycolysis which are reversible plus four additional reactions that circumvent the irreversible nonequilibrium reactions. 

Kidney Excretion and glu-coneogenesis Gluconeogenesis Free fatty acids, lactate, glycerol Glucose Glycerol kinase, phosphoenolpyruvate carboxy kinase... 

Six compounds have vitamin Bg activity (Figure 45-12) pyridoxine, pyridoxal, pyridoxamine, and their b -phosphates. The active coenzyme is pyridoxal 5 -phos-phate. Approximately 80% of the body s total vitamin Bg is present as pyridoxal phosphate in muscle, mostly associated with glycogen phosphorylase. This is not available in Bg deficiency but is released in starvation, when glycogen reserves become depleted, and is then available, especially in liver and kidney, to meet increased requirement for gluconeogenesis from amino acids. 

Major amino acids emanating from muscle are alanine (destined mainly for gluconeogenesis in liver and forming part of the glucose-alanine cycle) and glutamine (destined mainly for the gut and kidneys). 

Gluconeogenesis Formation of glucose from precursors other than carbohydrates (especially by the liver and kidney) using amino acids from proteins, glycerol from fats, or lactate produced by muscle during anaerobic glycolysis. 

The synthesis of glucose from noncarbohydrate sources is referred to as the gluconeogenesis. It is feasible only in certain organism tissues. The major site for gluconeogenesis is the liver. To a lesser extent, the kidneys and intestinal mucosa are involved in this process. 

Noncarbohydrate Sources for Gluconeogenesis. In addition to pyruvate and lactate, which are delivered to the liver and kidneys, other noncarbohydrate compounds serve as substrates for glucose synthesis. In accordance with the gluconeogenesis scheme, it may be anticipated that all materials of noncarbohydrate nature that are... 

Gluconeogenesis. The gluconeogenic pathway is present in the kidney, as in the liver. Thus, amino acids (and lactate) can be converted to glucose in the kidney but a major precursor, in acidotic conditions, is glutamine. 

Full details of the reaction are given in Appendix 8.4 and a detailed discussion of the role of the kidney in regulation of the acid/base balance is given in (Appendix 13.4). The oxoglutarate produced from these successive reactions is either oxidised to yield ATP or, under conditions of starvation, converted to glucose via gluconeogenesis (Figure 8.26). 

The main precursors of gluconeogenesis in the liver are lactate from anaerobically working muscle cells and from erythrocytes, glucogenic amino acids from the digestive tract and muscles (mainly alanine), and glycerol from adipose tissue. The kidney mainly uses amino acids for gluconeogenesis (Glu, Gin see p.328). 

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