Glycogen oxidation

To figure out the biological meaning of the crossover (Figure 2.9 (C-E)), we need to know why this occurs. In mammals the answer seems to be a simple conseqence of power obtainable from different metabolic pathways maximum ATP turnover rates supported by fat oxidation in mammals are only about two-thirds the maximum ATP turnover rates supportable by glycogen oxidation (figure 2.10). The reasons for... 

FIGURE 5-9 Respiratory quotient prior to exercise, during bicycling, and during a subsequent recovery period. The RQ increases with exercise, indicating a shitt from fat oxida-tion to glycogen oxidation. (Reprinted with permission from Murray el ai 1977,)... 

For a given physiologic environment, the heart selects the most efficient substrate for energy production. A fitting example is the switch from fatty acid to carbohydrate oxidation with an acute work jump or increase in workload.15 The transient increase in rates of glycogen oxidation is followed by a sustained increase in rates of glucose and lactate oxidation (Fig. 2). Because oleate oxidation remains unaffected by the work jump, the increase in 02 consumption and cardiac work are entirely accounted for by the increase in carbohydrate oxidation. 

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 ... 

Corticosteroids a chronic painless myopathy associated with the long-term use of corticosteroids is a particularly common example of drug-induced muscle disorder. It is almost certain that mild cases are overlooked because steroids are so frequently used to treat inflammatory myopathies such as polymyositis. Fluorinated steroids are particularly frequently implicated, and the incidence of drug-induced muscle disease is dose and time-related. The presence of muscle weakness can even complicate topical steroid therapy. Corticosteroid-induced myopathy is mediated via intramuscular cytosolic steroid receptors. The steroid-receptor complexes inhibit protein synthesis and interfere with oxidative phosphorylation. The myopathy is associated with vacuolar changes in muscle, and the accumulation of cytoplasmic glycogen and mitochondrial aggregations. 

Enzymes of glycogenes Glycogen synthase system is,glycoiy T sis, and py T ruvate oxidation Insulin Insulin Glucose 6-phosphate Glucagon (cAMP) phos-phorylase, glycogen... 

In starvation, glucose must be ptovided for the brain and erythrocytes initially, this is supphed from hver glycogen reserves. To spare glucose, muscle and other tissues reduce glucose uptake in response to lowered insuhn secretion they also oxidize fatty acids and ketone bodies preferentially to glucose. 

The ATP required as the constant energy source for the contraction-relaxation cycle of muscle can be generated (1) by glycolysis, using blood glucose or muscle glycogen, (2) by oxidative phosphorylation, (3) from creatine... 

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