Amino Acid Metabolism

Amino Acid Metabolism - Chapter 26 Chapter 26 Amino Acid...

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Unformatted text preview: Chapter 26 Chapter 26 Amino Acid Metabolism Overview of amino acid catabolism Transamination PLP is the coenzyme for the transamination Transamination Overall process of the transamination The glucose-alanine cycle transports nitrogen to the liver transports nitrogen to the liver Oxidative deamination by glutamate dehydrogenase Oxidative deamination by glutamate dehydrogenase Removed by the urea cycle Excretion of the excess nitrogen Aquatic animals Terrestrial vertebrates Birds and terrestrial reptiles The overall urea cycle reaction The urea cycle Generation of carbamoyl phosphate E. coli carbamoyl phosphate synthetase (CPS) Conversion of citrulline to argininoacuccinate Regulation of the urea cycle • Long-term regulation – The rates of synthesis of the four urea cycle enzymes and carbamoyl the four urea cycle enzymes and carbamoyl phosphate synthetase I (CPS I) in the liver: these enzymes are highly expressed in starving animals and in animals on very-high-protein diets • Short-term regulation – CPS I is allosterically activated by N-acetylglutamate – The urea cycle enzymes are controlled by the concentration of their substrates Synthesis of N-acetylglutamate and its activation of CPS I act The catabolic fates of amino acids • Glucogenic amino acids are degraded to pyruvate pyruvate, α-ketoglutarate, succinyl-CoA, succinyl fumarate, or oxaloacetate, each of which is a glucose precursor glucose precursor • Ketogenic amino acids are broken down to acetyl-CoA or acetoacetate, each of which is a fatty acid or ketone body precursor Glucogenic amino acids Ketogenic amino acids Six amino acids are degraded to pyruvate Serine dehydratase reaction: β-elimination Threonine can also be converted to acetaldehyde and glycine to acetaldehyde and glycine Asparagine and aspartate are coverted to oxaloacetate co to Five amino acids are converted to α-ketoglutarate Four amino acids are converted to succinyl-CoA Seven amino acids are degraded to acetyl-CoA Tetrahydrofolate as one-carbon carrier Conversion of one-carbon units on THF Branched-chain amino acids Essential and nonessential amino acids • Essential amino acids are synthesized by pathways that are present only in plants and microorganisms amino • Nonessential amino acids can be synthesized from common common intermediates Biosynthesis of nonessential amino acids: alanine, aspa aspartate, asparagine, glutamate, and glutamine aspa Biosynthesis of nonessential amino acids: arginine and proline Biosynthesis of nonessential amino acids: serine,cysteine,and glycine Biosynthesis of essential amino acids: lysine, methionine, and threonine Biosynthesis of essential amino acids: valine, leucine and isoleucine Biosynthesis of essential amino acids: aromatic amino acids ac Biosynthesis of essential amino acid: histidine Heme biosynthesis Heme degradation Synthesis of dopamine and catechol amine hormones hormones Synthesis of GABA and histamine Synthesis of serotonin Synthesis of glutathione Synthesis of nitric oxide Nitric oxide is the signal for vasodilation Nitrogen fixation by diazotrophs N2 + 8 H+ + 8 e- + 16 ATP + 16 H2O → 2 NH3 + H2 + 16 ADP + 16 Pi ...
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