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oxaloacetate + 3NADPH + NH 3 + 3ATP ---> threonine + 3NADP + + 3ADP + 3P i

oxaloacetate + 3NADPH + NH 3 + 3ATP ---> threonine + 3NADP + + 3ADP + 3P i. gamma lyase/beta synthase. Threonine can be degraded in three ways. (1) Threonine dehydrogenase pathway. Threonine Dehydrogenase. Must break C  -C  bond on an amino acid and stabilize a carbanion.

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oxaloacetate + 3NADPH + NH 3 + 3ATP ---> threonine + 3NADP + + 3ADP + 3P i

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  1. oxaloacetate + 3NADPH + NH3 + 3ATP ---> threonine + 3NADP+ + 3ADP + 3Pi

  2. gamma lyase/beta synthase

  3. Threonine can be degraded in three ways (1) Threonine dehydrogenase pathway Threonine Dehydrogenase

  4. Must break C-C bond on an amino acid and stabilize a carbanion

  5. 2-amino--ketobutyrate lyase

  6. What happens to the glycine? Glycine Cleavage System: trifunctional enzyme STEP1: decarboxylation of glycine

  7. STEP 2: formation of N5,N10-methylene-THF THF N5,N10-methylene-THF

  8. STEP 3: regeneration of catalytic site NADH NAD+

  9. There is another pathway of glycine degradation From glycine cleavage system Combine the glycine cleavage system with a reverse of the serine hydroxymethyltransferase rxn

  10. So…2 glycine = 1 serine + NADH + NH3

  11. If: 2 Gly = serine + NADH + NH3 If: Ser = pyruvate + NH3 Then: 2 Gly = pyruvate + NADH + 2 NH3 If: Pyruvate = 4 NADH + GTP + FADH2 Then: 2 Gly = 5 NADH + GTP + FADH2 + 2 NH3 If: NADH = 3 ATP GTP = ATP FADH2 = 2 ATP NH3 = -2 ATP Then: 2 Gly = 14 ATP, 1 Gly = 7 ATP

  12. So… Thr = Gly + Acetyl-CoA + NADH If: glycine is degraded by glycine cleavage system you get 1 N5,N10-methylene tetrahydrofolate, NH3 and NADH Then: Thr = N5,N10-THF + NH3 + 2 NADH + Acetyl-CoA If Acetyl-CoA = 3 NADH + GTP + FADH2 Then: Thr = N5,N10-THF + NH3 + 5 NADH + GTP + FADH2 If NADH = 3 ATP GTP = ATP FADH2 = 2 ATP NH3 = -2 ATP Then: Thr = N5,N10-THF + 16 ATP

  13. If: 2 Thr are degraded to 2 Gly Then: 2 Thr = 2 Gly + 2 NADH + 2 Acetyl-CoA If: 1 Gly = N5,N10- THF + 1 NH3 + 1 NADH by glycine cleavage system And 1 Gly + N5,N10-methylene tetrahydrofolate = serine by serine hydroxymethyltransferase Then: 2 Thr = 1 NH3 + 3 NADH + 2 Acetyl-CoA + serine If: Ser = pyruvate + NH3 Then: 2 Thr = 2 NH3 + 3 NADH + 2 Acetyl-CoA + pyruvate If: Acetyl-CoA = 3 NADH + GTP + FADH2 Pyruvate = 4 NADH +GTP + FADH2 Then: 2 Thr = 2 NH3 + 13 NADH + 3GTP + 3 FADH2 If: GTP = ATP, NADH = 3 ATP FADH2 = 2 ATP and NH3 = -2 ATP Then: 2 Thr = 44 ATP, Thr = 22 ATP

  14. (2) Threonine can be degraded by serine hydroxymethyltransferase

  15. What happens to acetaldehyde: can’t be put onto THF NAD+ NADH Acetaldehyde dehydrogenase Thr = glycine + Acetyl-CoA + NADH

  16. Thus: Thr = Gly + Acetyl-CoA + NADH If: glycine is degraded by glycine cleavage system you get 1 N5,N10-methylene tetrahydrofolate, NH3 and NADH Then: Thr = N5,N10-THF + NH3 + 2NADH + Acetyl-CoA If Acetyl-CoA = 3 NADH + GTP + FADH2 Then: Thr = N5,N10-THF + NH3 + 5 NADH + GTP + FADH2 If NADH = 3 ATP GTP = ATP FADH2 = 2 ATP NH3 = -2 ATP Then: Thr = N5,N10-THF + 16 ATP

  17. (3) Threonine can be converted to -ketobutyrate by threonine (serine) dehydratase

  18. What happens to -ketobutyrate? -ketobutyrate dehydrogenase Same mechanism as pyruvate dehydrogenase and -ketoglutarate dehydrogenase.

  19. NAD+ NADH Thr = propionyl-CoA + NADH

  20. What happens to propionyl-CoA?: Propionyl-CoA carboxylase Loss of ATP!

  21. Methylmalonyl-CoA epimerase: Why?

  22. Stability order of radicals allylic > R3C > R2CH > RCH2 > CH3 > vinylic

  23. So… Thr = succinyl-CoA - ATP + NADH If: Succinyl-CoA = malate + GTP + FADH2 Then: Thr = malate + GTP - ATP + NADH + FADH2 If: GTP = ATP Then: Thr = malate + NADH + FADH2 If: Malate = pyruvate + NADPH - NADH Then: Thr = FADH2 + pyruvate + NADPH If: Pyruvate ---> 4 NADH + GTP + FADH2 Then: Thr = 4NADH + GTP + 2 FADH2 + NADPH If GTP = ATP, NADH = 3 ATP FADH2 = 2 ATP and NH3 = -2 ATP Then: Thr = 17 ATP + NADPH

  24. Degradation of glycine by this pathway makes 1 N5,N10-methylene tetrahydrofolate, NH3 and NADH If: NADH is 3 ATP but NH3 is -2 ATP Then: Gly = 1 ATP + 1 N5,N10-THF

  25. Asp semialdehyde lysine threonine/methionine

  26. methionine O-succinylhomoserine homoserine O-phosphohomoserine threonine

  27. oxaloacetate + 3NADPH + 2ATP + succinyl-CoA + cysteine + N5-methyl-THF ---> methionine + succinate + pyruvate + 3NADP+ + 2ADP + 2Pi N5-methyl-THF comes from serine ---> glycine + N5,N10-methylene THF N5,N10-methylene THF + NADH ---> N5-methyl THF + NAD+

  28. 2 ways to degrade serine. (1) Serine dehydratase breaks the C-C bond

  29. Serine is converted to pyruvate + NH3 at no cost

  30. So: Ser = pyruvate + NH3 If: Pyruvate = 4 NADH + 1 FADH2 + GTP Then: Ser = 4 NADH + FADH2 + GTP + NH3 If: NADH = 3 ATP GTP = ATP FADH2 = 2 ATP NH3 = -2 ATP Then: Ser = 13 ATP

  31. (2) Serine hydroxymethyltransferase: bifunctional enzyme STEP 1: formation of glycine

  32. What happens to formaldehyde? STEP 2: formation of N5,N10-methylene-THF Serine hydroxymethyl transferase can be run in reverse to make serine from glycine and N5,N10-methylene THF

  33. 3-phosphoglycerate + NAD+ + NADPH + NH4+ + ATP ---> Serine + NADH + NADP+ + ADP + 2Pi 3-phosphoglycerate + NAD+ + NADPH + NH4+ + ATP + THF ---> glycine + NADH + NADP+ + ADP + 2Pi + N5,N10-methylene THF Reverse the glycine cleavage system CO2 + NH4+ + N5,N10-methylene THF + NADH ---> Glycine + THF + NAD+

  34. What happens to glycine? Glycine Cleavage System: trifunctional enzyme STEP1: decarboxylation of glycine

  35. STEP 2: formation of N5,N10-methylene-THF THF N5,N10-methylene-THF

  36. STEP 3: regeneration of catalytic site NADH NAD+ So…degradation of serine with serine hydroxymethyltransferase followed by the glycine cleavage system makes 2 N5,N10-methylene-THF, NH3 and NADH If: NADH is 3 ATP but NH3 is -2 ATP Then: Ser = 1 ATP + 2 N5,N10-THF

  37. Degradation of glycine by this pathway makes 1 N5,N10-methylene tetrahydrofolate, NH3 and NADH If: NADH is 3 ATP but NH3 is -2 ATP Then: Gly = 1 ATP + 1 N5,N10-THF

  38. There is another pathway of glycine degradation From glycine cleavage system Combine the glycine cleavage system with a reverse of the serine hydroxymethyltransferase rxn

  39. So…2 glycine = 1 serine + NADH + NH3

  40. If: 2 Gly = serine + NADH + NH3 If: Ser = pyruvate + NH3 Then: 2 Gly = pyruvate + NADH + 2 NH3 If: Pyruvate = 4 NADH + GTP + FADH2 Then: 2 Gly = 5 NADH + GTP + FADH2 + 2 NH3 If: NADH = 3 ATP GTP = ATP FADH2 = 2 ATP NH3 = -2 ATP Then: 2 Gly = 14 ATP, 1 Gly = 7 ATP

  41. Cysteine is degraded by 2 pathways (1) Oxidation by cysteine dioxygenase

  42. So…Cys = pyruvate + NH3 If: Pyruvate = 4 NADH + GTP + FADH2 Then: Cys = 4 NADH + GTP + FADH2 + NH3 If GTP = ATP NADH = 3 ATP FADH2 = 2 ATP H3 = -2 ATP Then: Cys = 13 ATP However…..

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