Amino Acid Catabolism of Carbon Skeletons

Amino Acid - Molecular Biochemistry II Amino Acid Catabolism Carbon Skeletons Copyright 1999-2007 by Joyce J Diwan All rights reserved Amino Acid

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Amino Acid Catabolism: Carbon Skeletons Copyright © 1999-2007 by Joyce J. Diwan. All rights reserved. Molecular Biochemistry II
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Amino Acid Carbon Skeletons Amino acids , when deaminated, yield α -keto acids that, directly or via additional reactions, feed into major metabolic pathways (e.g., Krebs Cycle). Amino acids are grouped into 2 classes, based on whether or not their carbon skeletons can be converted to glucose: glucogenic ketogenic .
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Carbon skeletons of glucogenic amino acids are degraded to: pyruvate , or a 4-C or 5-C intermediate of Krebs Cycle . These are precursors for gluconeogenesis . Glucogenic amino acids are the major carbon source for gluconeogenesis when glucose levels are low. They can also be catabolized for energy , or converted to glycogen or fatty acids for energy storage .
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Carbon skeletons of ketogenic amino acids are degraded to: acetyl-CoA , or acetoacetate . Acetyl CoA, & its precursor acetoacetate, cannot yield net production of oxaloacetate, the gluconeogenesis precursor. For every 2-C acetyl residue entering Krebs Cycle, 2 C leave as CO 2 . Carbon skeletons of ketogenic amino acids can be catabolized for energy in Krebs Cycle, or converted to ketone bodies or fatty acids . They cannot be converted to glucose .
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The 3-C α -keto acid pyruvate is produced from . Alanine deamination via Transaminase directly yields pyruvate. alanine α -ketoglutarate pyruvate glutamate Aminotransferase (Transaminase) COO - CH 2 CH 2 C COO - O CH 3 HC COO - NH 3 + COO - CH 2 CH 2 HC COO - NH 3 + CH 3 C COO - O + +
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Serine is deaminated to pyruvate via Serine Dehydratase. Glycine , which is also product of threonine catabolism, is converted to serine by a reaction involving tetrahydrofolate (to be discussed later). HO CH 2 H C COO - NH 3 + C COO - O H 2 O NH 4 + C COO - NH 3 + H 2 C H 3 C H 2 O serine aminoacrylate pyruvate Serine Dehydratase
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The 4-C Krebs Cycle intermediate oxaloacetate is produced from . Aspartate transamination yields oxaloacetate . Aspartate is also converted to fumarate in Urea Cycle. Fumarate is converted to oxaloacetate in Krebs cycle. aspartate α -ketoglutarate oxaloacetate glutamate Aminotransferase (Transaminase) COO - CH 2 CH 2 C COO - O COO - CH 2 HC COO - NH 3 + COO - CH 2 CH 2 HC COO - NH 3 + COO - CH 2 C COO - O + +
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Asparagine loses the amino group from its R-group by hydrolysis catalyzed by Asparaginase . This yields aspartate, which can be converted to oxaloacetate, e.g., by transamination. C CH 2 HC COO - NH 3 + O H 2 N COO - CH 2 HC COO - NH 3 + H 2 O NH 4 + asparagine aspartate Asparaginase
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4-C Krebs Cycle intermediate succinyl-CoA is produced from isoleucine, valine, & methionine. Propionyl-CoA
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This note was uploaded on 09/25/2010 for the course BCH 4024 taught by Professor Allison during the Spring '08 term at University of Florida.

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Amino Acid - Molecular Biochemistry II Amino Acid Catabolism Carbon Skeletons Copyright 1999-2007 by Joyce J Diwan All rights reserved Amino Acid

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