Liver glycogen from

Figure 1 Typical in wVo iH-decoupled MRS spectra at 22.5 MHz of the C-1 position of liver glycogen from a control subject (A) and from a type II diabetic patient (B) 4 hours after a liquid meal. Reproduced with permission from Magnusson I, Rothman DL, Katz LD, Shulman RG and Shulman Gl (1992) Increased rate of gluconeogenesis in type II diabetes mellitus. Journal of Clinical Investigation 90 1323-1327.

Even though acetate units, such as those obtained from fatty acid oxidation, cannot be used for net synthesis of carbohydrate in animals, labeled carbon from " C-labeled acetate can be found in newly synthesized glucose (for example, in liver glycogen) in animal tracer studies. Explain how this can be. Which carbons of glucose would you expect to be the first to be labeled by "Relabeled acetate ... 

McGarry JD et al From dietary glucose to liver glycogen the full circle round. Annu RevNutr 1987 7 51. 

Glucose is also formed from liver glycogen by glycogenolysis (Chapter 18). 

Anabolism The biosynthesis of complex molecules (chemicals) from simpler ones (e.g., glycogen from glucose in the liver). 

The effect of alkali treatment on molecular weight (compare with the case of the starch components) has been studied treating a 5% solution of rabbit-liver glycogen in 2 N sodium hydroxide, for 90 minutes at 100°, decreased the sedimentation constant (Sits X 1013) from 86 to 57 (that is, by 34%).237... 

Figure 6.19 Regulation of the synthesis of glycogen from glucose in liver and muscle. Insulin is the major factor stimulating glycogen synthesis in muscle it increases glucose transport into the muscle and the activity of glycogen synthase, activity which is also activated by glucose 6-phosphate but inhibited by glycogen. The latter represents a feedback mechanism and the former a feedforward. The mechanism by which glycogen inhibits the activity is not known. The mechanism for the insulin effect is discussed in Chapter 12.

A variety of fuels are available to generate ATP for muscle activity phosphocreatine glycogen (which can be converted to lactic acid or completely oxidised to CO2) glucose (from liver glycogen, transported to the muscle via the blood and completely oxidised to CO2) triacylglycerol within the muscle (completely oxidised to CO2) and fatty acids from triacylglycerol in adipose tissue (completely oxidised to CO2). 

Blood-bome fuels are glucose, which is derived from liver glycogen, and fatty acids derived from adipose tissue. Uptake depends on the flow of blood through the muscle, the concentration of the fuel in the blood and the demand for ATP within the muscle. During sustained exercise the flow of blood to the muscle can increase up to 50-fold and the rate of utilisation of the fuel can increase to a similar extent, yet the concentration of the fuels in blood remains remarkably constant (Table 13.5). 

Not surprisingly, the intake of sufficient carbohydrate to satisfy this demand is vital. If carbohydrate intake is low, glucose is provided in the short term (<24 hours in the adult) by breakdown of liver glycogen. After this period, glucose must be synthesised via the process of gluconeo-genesis primarily from amino acids released from the breakdown of muscle protein and from glycerol released... 

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