33 AAs - Fates BCAA

33 AAs - Fates BCAA - Amino Acids and Proteins: Metabolism:...

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Amino Acids and Proteins: Metabolism: Amino Acid Fates HNFE 3025 Fall 2009
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Skeletal muscle: takes up amino acids from the blood, especially glutamate is a net producer of alanine and glutamine uses amino acids primarily for protein synthesis is the primary site for the initial degradation of the BCAAs also releases a little bit of ammonia (actually NH 4 + ), but this release increases markedly when skeletal muscle is intensely active AA Metabolism in Skeletal Muscle 2
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leucine (Leu) Leucine, isoleucine and valine The most common essential amino acids in body protein ~ 35-40% of EAAs in dietary protein 14-18% of total proteins in skeletal muscle Help to maintain skeletal muscle mass (particularly leucine), especially in conditions of compromised function Starvation, immobilization, space flight, chronic heart failure BCAAs are catabolized in skeletal muscle to a far greater extent than liver Liver poorly expresses the initial transamination enzyme – Branched Chain Aminotransferase (BCAT) Branched Chain Amino Acids (BCAAs) 3 valine (Val) isoleucine (Ile)
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The initial reaction in the catabolism of the BCAAs uses α-KG for transfer of amino group recognizes all three BCAAs BCAT is located in the cytoplasm and the mitochondria Mitochondrial isoform is ubiquitous (except in the liver) Other tissues with relatively high activity include heart, kidney, diaphragm and adipose tissue Cytosolic isoform thought to be isolated to central and peripheral nervous system Branched Chain Aminotransferase (BCAT) 4
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The products of this reaction are branch chain- keto acids (BCKA) Can remain in muscle for further oxidation Can leave the cell and be transported in blood (bound to albumin) to other tissues for either re-amination or oxidation BCAT is reversible (like all aminotransferases), but the reaction is driven in the direction of Glu formation BCKAs are irreversibly degraded by the next step, oxidative decarboxylation Branched Chain Aminotransferase (BCAT) 5
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BCAAs α-Ketoglutarate Branched chain keto acids Glutamate BCAT BCAA Metabolism in Skeletal Muscle BCAA = branched chain amino acids (leucine, isoleucine and valine). BCAT (Branched Chain AminoTransferase) is found in mitochondria 6
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The second reaction, and the main regulatory point, in the catabolism of the BCAAs A multi-enzyme complex, with several coenzymes [like those of pyruvate dehydrogenase (PDH)] .
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33 AAs - Fates BCAA - Amino Acids and Proteins: Metabolism:...

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