1. Catabolism of the Carbon Skeletons of Amino Acids

2. Excess amino acids are catabolized to amphibolic intermediates used as sources of energy or for carbohydrate and lipid biosynthesis.
Initial reaction
Transamination
Remove any additional nitrogen
Hydrocarbon skeleton

3. Amphibolic intermediates formed from the carbon skeletons of amino acids.

4. Transamination typically initiates amino acid catabolism
Except
Proline, hydroxyproline, threonine, and lysine.

5. Catabolism of L-asparagine and of L-glutamine to amphibolic intermediates.

6. Ornithine Ornithine-aminotransferase
Elevate plasma and urinary ornithine
Gyrate atrophy of the retina
Hyperornithinemia- hyperammonemia syndrome
Defective mitochondrial ornithine-citrulline antiporter

7. Catabolism of arginine

8. Catabolism of proline.

9. Type I hyperprolinemia Type II hyperprolinemia
Proline dehydrogenase
Type II hyperprolinemia
Glutamate-semialdehyde dehydrogenase
Δ1-pyrroline-3-hydroxy-5-carboxylate is excreted.

10. Catabolism of histidine.

11. Disorders of histidine catabolism
Impaired histidase
Histidinemia
Urocanic aciduria
Folic acid deficiency
Figlu is excreted

12. Interconversion of serine and glycine

13. Reversible cleavage of glycine by the
mitochondrial glycine synthase complex.

14. Primary hyperoxaluria
Glycinuria
Defect in renal tubular reabsorption
Primary hyperoxaluria
Failure to catabolize glyoxylate formed by deamination of glycine.
Oxalate
Urolithiasis, nephrocalcinosis
Renal failure, hypertension

15. The cystine reductase reaction.

16. Catabolism of L-cysteine via the cysteine
sulfinate pathway

17. Catabolism of L-cysteine via the 3-mercaptopyruvate pathway

18. abnormalities of cysteine metabolism
Cystine-lysinuria (cystinuria)
Defect in renal reabsorption
Cystinosis
Deposition of cystine crystals in tissues
Homocystinuria
Cardiovascular disease

19. Mixed disulfide of cysteine and homocysteine.

20. Conversion of threonine to glycine and acetyl-CoA.

21. Intermediates in L-hydroxyproline catabolism

22. Hyperhydroxyprolinemia Type II hyperprolinemia
4-hydroxyproline dehydrogenase
Type II hyperprolinemia
Second dehydrogenase

23. Intermediates in tyrosine catabolism.

24. Tyrosine metabolic disorders
Type I tyrosinemia (tyrosinosis)
fumarylacetoacetate hydrolase
Type II tyrosinemia (Richner-Hanhart syndrome)
Tyrosine aminotransferase
Neonatal tyrosinemia
Lowered p-hydroxyphenylpyruvate hydroxylase activity

25. Alkaptonuria Homogentisate oxidase
The urine darkens on exposure to air
arthritis and connective tissue pigmentation (ochronosis)

26. Phenylalanine metabolic disorders
Hyperphenylalaninemias
Type I, classic phenylketonuria or PKU)
Defects in phenylalanine hydroxylase
Types II and III
defects in dihydrobiopterin reductase
Types IV and V
Defects in dihydrobiopterin biosynthesis
DNA probes facilitate prenatal diagnosis
Mental retardation

27. Alternative pathways of phenylalanine
catabolism in phenylketonuria

28. Catabolism of L-lysine.

29. Periodic hyperlysinemia
Lysine competitively inhibits liver arginase
Hyperammonemia

30. Catabolism of L-tryptophan

31. Formation of xanthurenate in vitamin
B6 deficiency

32. Hartnup disease
Impaired intestinal and renal transport of tryptophan and other neutral amino acids

33. Formation of S-adenosylmethionine

34. Conversion of methionine to propionyl- CoA

35. branched-chain –keto acid dehydrogenase
The initial reactions are common to all three branched-chain amino acids
branched-chain –keto acid dehydrogenase
Multimeric enzyme complex
A decarboxylase,
a transacylase
a dihydrolipoyl dehydrogenase
Being inactivated by phosphorylation

36. The analogous first three reactions in the catabolism of leucine, valine, and isoleucine.

37. METABOLIC DISORDERS OF BRANCHEDCHAIN AMINO ACID CATABOLISM
Maple syrup urine disease (branched-chain ketonuria)
α-keto acid decarboxylase complex
Plasma and urinary levels of leucine, isoleucine, valine, α-keto acids, and α-hydroxy acids (reduced α-keto acids) are elevated
Isovaleric acidemia
Isovaleryl-CoA dehydrogenase

38. Catabolism of the β-methylcrotonyl-
CoA formed from L-leucine

39. Subsequent catabolism of the tiglyl-
CoA formed from L-isoleucine.

40. Subsequent catabolism of the
methacrylyl-CoA formed from L-valine

41. Summary
Excess amino acids are catabolized to amphibolic intermediates used as sources of energy or for carbohydrate and lipid biosynthesis.
Initial reaction
Transamination
Remove any additional nitrogen
Hydrocarbon skeleton
To amphibolic intermediates

42. Metabolic diseases associated with glycine catabolism
Glycinuria
Primary hyperoxaluria
Metabolic disorders of cysteine catabolism
Cystine-lysinuria,
Cystine storage disease,
Homocystinurias

43. Metabolic diseases of tyrosine catabolism
Tyrosinosis,
Richner-Hanhart syndrome,
Neonatal tyrosinemia,
Alkaptonuria
Metabolic disorders of phenylalanine catabolism
Phenylketonuria (PKU)
Several hyperphenylalaninemias.

44. Metabolic diseases of lysine catabolism
Hyperlysinemiaammonemia
Forms
Periodic
Persistent

45. Metabolic disorders of branched-chain amino acid catabolism
Hypervalinemia
Maple syrup urine disease
Intermittent branched-chain ketonuria
Isovaleric acidemia
Methylmalonic aciduria