Amino Acid Degredation Flashcards
Ketogenic
- Amino acids that are degraded to acetoacetyl-CoA / acetyl-CoA
- Will eventually form ketone bodies.
Glucogenic
- Amino acids that are degraded to pyruvate, α-ketoglutarate, succinyl-CoA, fumarate, and oxaloacetate
- Will eventually enter citric acid cycle
How many amino acids are ketogenic?
7
How many amino acids are glucogenic?
18
What are the ketogenic amino acids?
- Leucine
- Lysine
- Tyrosine
- Isoleucine
- Phenylalanine
- Threonine
- Tryptophan
What are the glucogenic amino acids?
- Alanine
- Arginine
- Asparagine
- Aspartate
- Cysteine
- Glutamine
- Glutamate
- Glycine
- Proline
- Serine
- Histidine
- Methionine
- Valine
What are the 5 amino acids that are both glucogenic and ketogenic?
- Tyrosine
- Isoleucine
- Phenylalanine
- Threonine
- Tyrptophan
What are the 2 exclusively ketogenic amino acids?
- Leucine
- Lysine
What enzymes play an important role in amino acid catabolism?
- Biotin
- THF
- S-adenosylmethionine (adoMet)
All specialize in one carbon transfer reaction
THF (Tetrahydrofolate)
- Two nitrogen atoms are important
- Carbon group undergoing transfer can be bonded to N5, N10 or both
- Three different forms
What are the three different forms of THF
- N5, N10-Methylene-THF
- N5-Methyl-THF
- N5, N10-Methenyl-THF
N5, N10-Methylene-THF
- Primary source of one carbon units comes from the breakdown of serine to glycine
- Transfers medium oxidized carbons (CH2OH)
- Is interconverted between N5-Methy-THF and N5, N10-Methenyl-THF
N5-Methy-THF
Transfers the most reduced carbon (CH3)
N5, N10-Methenyl-THF
Transfers a more oxidized carbon (CHO)
What is N10-Formyl-THF
Occurs when carbon atom comes from formate instead of serine
S-adenosylmethionine (adoMet)
- Preferred cofactor for transfer reactions involving methyl groups
- Synthesized by adenosine and methionine by THF
Describe the synthesis of adoMet
- Methionine + ATP get linked together to form SAM (S-adenosylmethionine)
- Methyl group from SAM gets transferred to an acceptor to form S-adenosylhomocysteine intermediate
- S-adenosylhomocysteine is broken down to homocysteine and adenosine
- Methyl group is transferred to homocysteine by N5-Methyl-THF in a reaction that is catalyzed by methionine synthase (this regenerates methionine)
- Methionine gets reconverted back into SAM
Biotin
Transfers carbon atoms from bicarbonate (HCO3-) in blood in a two step reaction
Describe the two step process that is necessary for the one carbon transfer reaction involving Biotin
Biotin is linked to the enzyme biotin carboxylase
- Step 1: Biotin reacts with bicarbonate + ATP to replace H on Nitrogen with a CO2 moiety
- Step 2: The CO2 moiety is transferred to another molecule
(ex: acetyl-CoA) producing a carboxylate group on that molecule
(ex: acetyl-CoA —> malonyl-CoA)
What amino acids are degraded to pyruvate?
- Alanine
- Glycine
- Cysteine
- Serine
- Threonine
- Tryptophan
What amino acids are degraded to α-ketoglutarate?
- Arginine
- Glutamate
- Glutamine
- Histidine
- Proline
What amino acids are degraded to succinyl-CoA?
- Isoleucine
- Methionine
- Threonine
- Valine
What amino acids are degraded to fumarate?
- Phenylalanine
- Tyrosine
What amino acids are degraded to oxaloacetate?
- Aspartate
- Asparagine
What are the branched chain amino acids?
- Leucine
- Isoleucine
- Valine
Describe the degradation of branched chain amino acids
- 2 Steps:
- Step 1:
Amino acid form —> Keto acid form (PLP aminotransferase reaction) - Step 2:
Keto acid form —> Final product (Acetyl-CoA, Succinyl-CoA, Acetoaceate) by BCKDH
This is an oxidative decarboxylation reaction
Maple syrup urine disease
- Defective BCKDH enzyme
- You cannot successfully metabolize branched chain amino acids which results in the accumulation of these amino acids and their “spill over” into the urine
- Result is thick sweet smelling urine
Describe the genetic defect that occurs as a result of the inability to break down phenylalanine
- Phenylalanine hydroxylase = first enzyme in the catabolic pathway for phenylalanine (breakdown of phenylalanine to tyrosine)
- A defect in the enzyme = PKU disease
- Result = elevated levels of phenylalanine in the blood
What happens in individuals who have PKU which results in elevated levels of phenylalanine in the blood?
- A normally little-used pathway is activated in which phenylalanine undergoes transamination with pyruvate to yield phenylpyruvate
- Phenylalanine and phenylpyruvate accumulate in blood and tissues impairing the normal development of the brain
