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Review Session

Review Session . Saturday, 3 pm PH 104. Chapter 27, Nitrogen Metabolism: 1. Deamination 2. Urea cycle 3. Conversion of aa carbon skeletons to common intermediates. First reaction in aa breakdown is always the removal of the - amino group.

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Review Session

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  1. Review Session Saturday, 3 pm PH 104

  2. Chapter 27, Nitrogen Metabolism: 1. Deamination 2. Urea cycle 3. Conversion of aa carbon skeletons to common intermediates.

  3. First reaction in aa breakdown is always the removal of the -amino group. Most are transaminated to -KG which then transaminates OAA to asp. Transaminases require PLP (vit B6). Actual deamination to ammonia occurs via glu DH.

  4. Figure 26-1 Forms of pyridoxal-5’-phosphate.(a) Pyridoxine (vitamin B6) and (b) Pyridoxal-5’-phosphate (PLP) (c) Pyridoxamine-5’-phosphate (PMP) and (d) The Schiff base that forms between PLP and an enzyme -amino group.. Page 986

  5. Figure 26-2 The mechanism of PLP- dependent enzyme-catalyzed transamination. Page 987

  6. Nucleophillic attack by aa-NH3 on Schiff base. E-Lys now free to act as general base. Tautomerization encouraged by removal of the H of aa by E-Lys and protonation of PLP

  7. (see animated figure) Step II: Conversion back to PMP requires reverse of these 3 steps “An electron pusher’s delight: Cleavage of any of the aa’s C bonds produces a resonance stabilized carbanion whose e- are delocalized onto PLP (the electron sink).

  8. Figure 26-3 The glucose–alanine cycle. Muscle aminotransferases accept pyruvate as their amino acceptor. Overall scheme transfers nitrogen to liver for urea cycle. Page 988

  9. Figure 26-4 The oxidative deamination of glutamate by glutamate DH. GluDH is allosterically inhibited by GTP and NADH; Activated by ADP, leu, and NAD+.

  10. Nitrogen Excretory Products: Ammonia Uric Acid Urea

  11. Page 992 Figure 26-7The urea cycle.

  12. Figure 26-8 The mechanism of action of CPS I. Allosterically activated by N-acetyl glu: produced by NAGlu synthase--it is a sensor for [glu]. Page 993 Hi [glu] means lots of aa breakdown.

  13. Figure 26-9X-Ray structure of E. coli carbamoyl phosphate synthetase (CPS). Small subunit 3 sites very far away from each other: Connected by long tunnel “Channeling”! Page 993

  14. Ornithine Transcarbamoylase Carbamoyl Phosphate + Ornithine  Citrulline + Pi Ornithine produced in the cytosol must be transferred to mito by specific transport system. Citrulline is transferred back out to the cytosol Ornithine looks like Lys but has one fewer C’s Thus the side chain amino group is  !!!!

  15. Figure 26-10 The mechanism of action of argininosuccinate synthetase. Displacement Activation 18O label Mechanistic support Reaction type? Page 994 Condensation

  16. Arginosuccinase: Arginosuccinate  Arg + Fumarate

  17. Arginase: Arg + H2O  Ornithine + Urea

  18. Figure 26-11 Degradation of amino acids to one of seven common metabolic intermediates. Page 995

  19. Chapter 27: Integration of Metabolism Problems 2-6

  20. Page 1055 Figure 27-1 The major energy metabolism pathways.

  21. Figure 27-2 The metabolic interrelationships among brain, adipose tissue, muscle, liver, and kidney. Page 1057

  22. “Alfonse, Biochemistry makes my head hurt!!” \

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