Amino Acids (Lecture 27) Flashcards
which amino acids require 1 step degradation and what are their products?
glutamate ->alpha ketoglutarate (via GDH)
aspartate -> oxaloacetate (via aspartate transaminase)
what are the 3 fates of amino acid catabolism?
gluconeogenic
ketogenic
gluconeo-ket-genic
what does gluconeogenic mean?
amino acids (carbon skeleton) will branch back into the CAC to generate glucose
what does ketogenic mean?
amino acids used to make ketone bodies
which amino acids require a conversion reaction (2 steps)?
GLUTAMINE:
glutamine->glutamate ->alpha KG
ASPARAGINE:
asparagine->aspartate->oxaloacetate
this occurs via a deamination reaction (1st step)
which amino acids are broken down in the urea cycle?
aspartate (combined with citruline) will be converted into arginosuccinate via ASS
arginosuccinate will then be broken down to fumarate and arginine via arginosuccinase
what do gluconeogenic aa do?
replenish the substrates involved in the citric acid cycle via anapleurotic reactions
what do ketogenic aa do?
aa will be broken down to acetyl coa and/or acetoacetate to then form beta-hydroxybutarate, to then serve as an energy source to the heart and brain (produce FADH2 and NADH)
where are branched chain amino acids degraded?
muscle, adipose, kidney and brain tissue
how are branched amino acids degraded?
the branched amino acids will undergo a transferase reaction via branched chain aminotransaminase to generate a keto-acid.
the alpha keto acid will then form acyl coa derivatives via branched chain alpha keto acid dehydrogenase complex (BCKD)
deficiency in BCKD causes…
maple syrup urine disease
how is BCKD regulated?
via phosphorylation by a kinase
the phosphorylation will inactivate the enzyme, and dephosphorylation activated the enzyme
the abundance of the branched chain (leucine) keto acids will inhibit BCKD
what is alanine synthesized from?
pyruvate via aminotransferase
what is aspartate synthesized from?
oxaloacetate via amino transferase
what is asparagine synthesized from?
oxaloacetate via amino transferase AND aspartate (and glutamine + ATP) via asparagine synthase
what is glutamate synthesized from?
alpha KG via aminotransferase
what is glutamine synthesized from?
alpha KG via aminotransferase AND glutamate (and ATP + NH4) via glutamine synthase
methionine metabolism
homocysteine needs a 1 carbon donor to produce methionine. This donor is 5-methyl-THF
this reaction occurs with the cofactor, vitamin B12
how is homocysteine metabolized?
homocysteine is converted to propionyl-coa (odd chain FA beta oxidation) and then will be converted into succinylcholine coa molecule, which will feed into the CAC
is methionine gluconeogenic, ketogenic or gluconeo-keto-genic AND why?
gluconeogenic because it replenishes succinylcholine coa for the CAC
hyper-homocysteinemia
imbalance between the rate of production/breakdown of homocysteine
what are causes of hyper-homocysteinemia
B12, folic acid deficiency
mutations in the enzyme converting homocysteine go cystathionine (cystathionine beta synthase) - causes accumulation of homocysteine
hyper-homocysteinemia is associated to…
cardiovascular disease
cognitive impairment/dementia
developmental defects (neural tube defects and anencephaly)
what is given to pregnant women to prevent developmental defects neural tube defects and anencephaly
folic acid to ensure that homocysteine is properly degraded
how is cysteine synthesized?
via a transsulfuration reaction:
homocysteine is combined with serine and PLP as a cofactor
another round with PLP will remove NH3 to form alpha keto butyrate and cysteine
