Week 3 Amino Acid Catabolism Flashcards
before an amino acid can be utilized for energy producition what must it be stripped of?
nitrogen content
The first step of AA catbolism is what?
transfer of the amino group (transamination) to alpha-ketogluterate to form Glutamate
what enzyme class facilitates the amino group transfer?
transaminases or aminotransferases
after Glu is made via transamination, what is its fate (2)
recycled to support new amino acid synthesis
deaminated and ammonium is formed
why is the released ammonia bad?
ammonia is a neurotoxin (can cross blood-brain barrier)
what is hyperammonemia
abnormal elevation of blood ammonia levels (can cause coma or death)
what is our bodies solution to limiting ammonia in our bodies?
ammonia is converted to non-toxic metabolites
how is ammonia “carried” in peripheral tissue?
ammonia is wither incorporated into precursor molecules to form glutamine or alanine
what enzyme is present in the liver and kidneys that converts glutamine (a carrier of ammonia) back to glutamate and ammonia?
glutaminase
where is the ultimate site of ammonia detoxification?
the liver
what is the detoxified form that ammonia is converted to in the liver? what is this biochemical pathway callled
urea. urea cycle
why is urea a good product for excretion?
no net charge, highly water soluble (very polar)
if there is little free AA, what happens to the urea cycle? why?
urea cycle decreases. AA allosterically regulate the urea cycle such that if there is not sufficient free AA, the cycle (and related protein degradation) does not occur
how much ATP is consumed for every molecule of Ammonia in the urea cycle?
3 ATP/ammonia
what is the strucutre of urea. where do the atoms come from?
NH2NH2CO (Carbon from CO2, N from ammonia, N from Asp)
other than urea, what is produced during urea cycle?
fumerate, this can be used for intermediary metabolism (including gluconeogenesis)
what is uremia?
an increase in Blood Urea Nitrogen (BUN) correlated with renal failure
what organ is responsible for excretion of urea from the blood?
kidneys
what causes hyperammonemia?
defect in liver fxn leading to failure to detoxify ammonia. can be congenital or acquired
what are some symptoms of hyperammonemia?
ammonia crosses blood-brain barrier and results in tremors, slurred speech, vomiting, coma, death
what is a congenital defect?
a defect present from birth
what is a potential cause of congenital hyperamonemia?
a genetic defect in any of the FIVE urea cycle enzymes
how many enzymes are used in the urea cycle
5
Symptoms of Congenital Urea Cycle Disorders (UCDs) tend to be more severe when which enzymes are affected? when do symptoms arise?
why?
more severe when enzymes earlier in the urea cycle are impacted (CPSI), symptoms arise 24 to 48 hours after birth, urea cycle is not needed in utero
how would you treat hyperammonemia? 2
restrict protein and supplement essential AA
create an alternative pathway for ammonia excretion
what is the alternate pathway for ammonium excretion?
oral Na benzoate or Na phenylbutyrate can complex with Gly or Glu (respecitvely) to form readily excretable water soluble adducts
how can hyperammonemia be acquired?
liver damage: alcohol abuse, hepatitis, fatty liver disease
what is hepatic encaphalopathy?
a condition caused by acquired hyperammonemia. neurolopsychiatric alterations and coma. seen in half of liver damage cases.
what is urease?
a protein produced by certain bacteria that converts urea to ammonia. this is problematic because it can result in kidney stones due to UTI
carbon skeletons of degraded AA (AA-Amino group) are classified as what?
ketogenic or glucogenic
what can glucogenic AA feed into?
feed into TCA, gluconeogenesis, non-essential AA synthesis
what can ketogenic AA feed into?
form Ac-CoA which can only feed into TCA, FA or ketone body synthesis (starvation)
every acetyl-CoA that feeds into the TCA cycle produces how much ATP
12 (this compensates for the 3 ATP needed to produce urea in urea cycle
Most non-essential AA are…why might this be?
glucogenic. probably an evoluiton advantage becuase all these AA can be readily enter intermidiary metabolis in a single step
what are the 6 wholly or partly ketogenic AA?
Leu, Lys (wholly)
Ile, Phe, Trp, Tyr
the ketogenic AA typically are broken down to…
Acetyl-CoA (cant be converted to pyruvated, enters TCA)
what are some metabolites that glucogenic AA are converted to?
pyruvate, oxaloacetate (NOT Acetyl-CoA)
