Gluconeogenesis recycling

This reaction is also exergonic (AG° = -25.1 moH = -6.0 kcal moH) as before, we need to multiply this value by 2 to hnd the energy yield for each molecule of glucose that enters the pathway. Lactate is a dead end in muscle metabolism, but it can be recycled in the liver to form pyruvate and even glucose by a pathway called gluconeogenesis ( new synthesis of glucose ), which we will discuss in Section 18.2. 

The sprint is essentially anaerobic and produces lactate from glucose by glycolysis. Lactate is then recycled to glucose by gluconeogenesis. 

Muscle tissue uses large quantities of glucose, producing lactate in the process. The liver is an important site of gluconeogenesis to recycle the lactate to glucose. 

Many hours after a meal, and also during starvation, glucose is removed from the blood by muscle and other tissues, and lactate is produced by them. This leads to an increase in the rate of gluconeogenesis from lactate by hepatocytes. The glucose that is produced this way, however, only constitues recycling of the carbon atoms and gluconeogenic enzymes also convert other 3-carbon compounds into glucose. 

Lactate is being produced continuously from glucose by anaerobic glycolysis in red blood cells, the retina and the kidney medulla. This lactate is recycled to glucose by a process known as the Cori cycle. The lactate is returned to the liver and is metabolised to glucose by gluconeogenesis in a process that consumes the equivalent... 

Katz, J. and J.A. Tayek, 1999. Recycling of glucose and determination of the Cori Cycle and gluconeogenesis. Am. J. Physiol. Endocrinol. Metab. 277, E401-407. 

Lee, W.N., S. Sorou and E. A Beigner. 1991. Glucose isotope, carbon recycling, and gluconeogenesis using [U- C] glucose and mass isotopomer analysis. Biochem. Med. Metab. Biol. 45, 298-309. 

Freidmann, B., Goodman, E. H., Jr., Saunders, H., Kostos, V., and Weirihouse, S., 1971, An estimation of pyruvate recycling during gluconeogenesis in the perfused rat liver. Arch. Biochem. Biophys. 143 566. 

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