Lecture 12 aa catabolism pt 2

Lecture 12 aa catabolism pt 2 - BergTymoczkoStryer...

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Biochemistry Chapter 23: Protein Turnover and Amino Acid Catabolism Copyright © by W. H. Freeman and Company   Berg • Tymoczko • Stryer
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Degradation of amino acids α -amino groups are converted into ammonium ions Transamination Oxidative deaminatio n
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α -amino group amino acid 1 α -ketoacid Transamination reaction α -ketoacid Amino acid 2
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α -amino group amino acid 1 α -ketoacid The recipient α -ketoacid is often α -ketoglutarate α -ketoacid Amino acid 2
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Transamination Reactions Often the first step in amino acid degradation (exceptions: serine/threonine) Reaction : the transfer an α -amino group from an α -amino acid to to an α -ketoacid ( usually α- ketoglutarate ) characteristic feature : a Schiff base intermediate Coenzyme : pyridoxal phosphate (electron sink/electrophilic catalyst) Significance : to funnel the amino groups to glutamate , one common intermediat
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Transaminati on Oxidative deamination Amino transferases Glutamate dehydrogenase Ammonia is toxic!!
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1) Synthesis of carbamoyl phosphate 2) The carbomoyl group is transferred to ornithine to form citrulline 3) Citrulline condenses with aspartate to form argininosuccinate 4) Argininosuccinate is cleaved to arginine and fumarate 5) Arginine is hydrolyzed to generate urea and ornithine 6) The cycle continues Toxic ammonium ions are excreted as urea via the urea cycle
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Carbamoyl phosphate synthetase Cofactor? Not this time! Step 1: Synthesis of carbamoyl phosphate
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Anhydride bond— high energy transfer potential Step 2: carbamoyl phosphate enters the cycle in a reaction with ornithine * Ornithine and citrulline are amino acids*
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From carbamoyl phosphate From aspartate Step 3: aspartate contributes another amino group
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N from carbamoyl phosphate N from aspartate Step 4: Formation of Arginine and Fumarate C-skeleton of aspartate
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Step 5: Urea
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This note was uploaded on 01/16/2012 for the course BIOLCHEM 415 taught by Professor Michaeluhler during the Fall '06 term at University of Michigan.

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Lecture 12 aa catabolism pt 2 - BergTymoczkoStryer...

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