Control of Carbohydrate Metabolism

Glucose is formed from pyruvate, which in turn can he obtained from lactate that accumulates in muscle during exercise. This process, called glu-coneogenesis, takes place in the liver after lactate is transported there hy the blood. The newly formed glucose is transported back to the muscles by the blood. 

Gluconeogenesis bypasses the irreversible reactions of glycolysis. Oxaloacetate is an intermediate in this pathway. 

How does control of key enzymes control carbohydrate metabolism  

These two processes are catalyzed by two enzyme activities on the same protein. These two enzyme activities are controlled by a phosphorylation/ dephosphorylation mechanism. Phosphorylation activates the enzyme that degrades F2,6P whereas dephosphorylation activates the enzyme that produces it. 

Inhibition of fructose-1,6AAiphosphatase by fructose-2,6A isphosphate. Proc. Nat l Acad, of Sci., U.S.A. 78 2861-2863.) 

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In parasitic flatworms, 5-HT serves a variety of functions from control of carbohydrate metabolism to intra- and interorganism (host-parasite) communication (36). Rhythmical movement is stimulated by 5-HT and related indoleamines (e.g., lysergic acid diethylamide) (7,8,37). This stimulatory effect, like the ACh inhibitory effect, can be obtained in the absence of the central ganglia suggesting a peripheral site of action (37). The stimulation of motility (increased contraction amplitude and frequency) in vitro suggests that 5-HT or a closely related indoleamine is an excitatory transmitter in both the trematodes F. hepatica (9, 37, 38), S. mansoni (11, 12, 39, 40), Clonorchis sinensis... 

Control of carbohydrate metabolism is important in physical activity of all sorts. 

What roles do the first and last steps of glycolysis play in control of carbohydrate metabolism ... 

FIGURE 18.11 Allosteric effects in the control of carbohydrate metabolism. The effect of AMP (0, 10, and 25 aM [micromolar]) on the inhibition of fructose-1,6-fe iphosphatase by fructose-2,6-fe iphosphate. Activity was measured in the presence of 10 pM fructose-1,6-fe sphosphate. (Adapted from Van Schaftingen, E., and H. G. Hers,... 

Some topics are discussed several times, such as the control of carbohydrate metabolism. Subsequent discussions make use of and build on information students have already learned. It is particularly useful to return to a topic after students have had time to assimilate and reflect on it. 

Pyruvate carboxylase Cytoplasm ATP, CO, ADP Acetyl- CoA Control of carbohydrate metabolism... 

Torres NV. Modeling approach to control of carbohydrate-metabolism during citric acid accumulation by Aspergillus niger. 1. Model definition and stabdity of the steady state. Biotechnol Bioeng 1994 44 104-11. 

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