Lecture_21_4-15-10-PDF_41722

Lecture_21_4-15-10-PDF_41722 - Amino Acid Metabolism (Lec...

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Amino Acid Metabolism (Lec 21) 5. Amino acid biosynthesis 6. Other products of amino acid metabolism 7. Nitrogen fixation
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All plants and some microorganisms can synthesize all 20 L-amino acids that occur in proteins. Essential amino acids Mammals require about half of them in their diet, and these are called the essential amino acids .
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All the nonessential amino acids (except tyr ) are synthesized from one of four common metabolic intermediates 1 2 3 Ala Asn Asp Glu Gln Pro Arg 4 Ser Cys Gly
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Tyrosine: misclassified as being nonessential (p 761) One-step hydroxylation of the essential Phe
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1 Syntheses of Ala, Asp, Glu, Asp, and Gln 2 3 Fig. 21-27
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Alanine becomes pyruvate as the amino group is transferred to a -KG. alanine a -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 + + Lec-20 Transaminases (aminotransferases) catalyze the reversible reaction . 1
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Lec-19 Transaminases (aminotransferases) catalyze the reversible reaction .
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There are multiple transaminase enzymes which vary in substrate specificity. 3 Lec-19
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2 Lec-19
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Gln is the amino group donor in the formation of many biosynthetic products as well as being a storage form of ammonia 2 example
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Glutamine synthetase is the most important enzyme for assimilation of nitrogen into biological molecules. + NH 4 + ADP + P i Overall reaction 5 (Fig 21-27 ) Glutamine synthetase ATP
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Glutamate dehydrogenase Don’t be confused between: Glu dehydrogenase and Glu synthetase Lec-19
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Regulation of Glutamine Synthetase (GS) in E. coli E. coli enzyme regulated by: (1) Cumulative feedback inhibition ( 9 allosteric inhibitors with additive effects) (2) Covalent modification (3) Regulation of enzyme synthesis
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(1) Cumulative feedback inhibition ( 9 allosteric inhibitors with additive effects)
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Regulation of E. coli GS by covalent modification Instead of phosphorylation, adenylation and uridinylation influences the enzyme.
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Regulation of E. coli GS by covalent modification 1 1 . PII is an enzyme that adenylates GS at a specific tyrosine. 2 . Adenylation makes GS less active . 2 3 . Uridylytransferase uridylylates the adenoyltransferase and makes the enzyme remove adenylyl group which in turn makes GS more active . 3 4 . Uridylyltransferase is activated by ATP and a -ketoglutarate and is inhibited by Glutamine and P i . 4
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Regulation of Glutamine Synthetase (GS) in E. coli E. coli enzyme regulated by: (1) Cumulative feedback inhibition (9 allosteric inhibitors with additive effects) (2) Covalent modification (3) Regulation of enzyme synthesis Long term activation by increasing transcript levels is also a factor 1. reduced transcription of glutamine synthetase when ammonium levels are adequate 2. increased transcription when ammonium levels are low
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Proline and Arginine are made from Glutamate Arginine is made through the urea cycle in the mitochondria
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Production of serine from the glycolysis intermediate 3-phosphoglycerate 4 Ser Cys Gly
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Lecture_21_4-15-10-PDF_41722 - Amino Acid Metabolism (Lec...

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