Muscle metabolic role

Another indication of the difference between the metabolic roles of muscle, a consumer tissue and liver, a contributer tissue, is the enzyme glucose-6-phospha-tase. This enzyme is required for the production of neutral glucose. It is present in liver and kidney but not in strict consumer tissues, such as muscle and brain. Without glu-cose-6-phosphatase the glucose-6-phosphate cannot be converted to dephosphorylated glucose, which is necessary for... 

Casey A and Greenhaff PL (2000) Does dietary creatine supplementation play a role in skeletal muscle metabolism and performance Amencaw Journal of Clinical Nutrition 72, 607S-17S. 

In contrast to arsenic, trace concentrations of selenium are essential for human and animal health. Until the late 1980s, the only known metabolic role for selenium in mammals was as a component of the enzyme glutathione peroxidase (GSH-Px), an anti-oxidant that prevents cell degeneration. There is now growing evidence, however, that a seleno-enzyme is involved in the synthesis of thyroid hormones (Arthur and Beckett, 1989 G. F. Combs and S. B. Combs, 1986). Selenium dehciency has been linked to cancer, AIDS, heart disease, muscular dystrophy, multiple sclerosis, osteoarthropathy, immune system and reproductive disorders in humans, and white muscle disease in animals (Levander,... 

Skeletal muscles use many fuels to generate ATP. The most abundant immediate source of ATP is creatine phosphate. ATP also can be generated from glycogen stores either anaerobically (generating lactate) or aerobically, in which case pyruvate is converted to acetyl CoA for oxidation via the TCA cycle. All human skeletal muscles have some mitochondria and thus are capable of fatty acid and ketone body oxidation. Skeletal muscles are also capable of completely oxidizing the carbon skeletons of alanine, aspartate, glutamate, valine, leucine, and isoleucine, but not other amino acids. Each of these fuel oxidation pathways plays a somewhat unique role in skeletal muscle metabolism. 

The regulation of mammalian adenylosuccinate synthetase is complicated. It is dependent on the isozyme content and levels in a given tissue as well as the effects of substrate and product levels. The two isozymes may have different metabolic roles either in AMP biosynthesis and interconversion, or in the functions of the purine nucleotide cycle. Most studies have considered kinetic parameters for the isolated enzyme and in only a few instances has regulation been studied in vivo. Sufficient information is available concerning the regulation of the basic isozyme in muscle to consider that enzyme in detail. Factors controlling the acidic isozyme are less clearly defined. 

Lomako, J. Lomako, W.M. Whelan, W.J. Glycogen metabolism in quail embryo muscle. The role of the glycogenin primer and the intermediate proglycogen. Ear. J. Biochem. 1995, 234, 343-349. 

Creatine is quantitatively the main component of the NPN fraction. This molecule plays an important role in fish muscle metabolism in its phosphorylated form it is absent in crustaceans and molluscs. 

Nucleotides and related compounds generally play an important role as coenzymes. They participate actively in muscle metabolism and supply... 

Although some 80% of the total body pool of vitamin Bg is associated with muscle glycogen phos-phorylase, this pool turns over relatively slowly. The major metabolic role of the remaining 20% of total body vitamin Bg, which turns over considerably more rapidly, is in amino acid metabolism. Therefore, a priori, it seems likely that protein intake will affect vitamin Bg requirements. People maintained on (experimental) vitamin Bg-deficient diets develop abnormalities of tryptophan and methionine metabolism faster, and their blood vitamin Bg falls more rapidly, when their protein intake is high. Similarly, dming repletion of deficient subjects, tryptophan and methionine metabolism and blood vitamin Bg are normalized faster at low than at high levels of protein intake. 

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