Nitrogen Turnover Flashcards
nitrogen compoounds are degraded into mostly
- urea
- urea levels are the only thing that changes in excretion with regards to proteins intake
excretion in urine comes in four forms
- ammonia
- urea
- uric acid (purine breakdown product)
- creatinine (proportional to muscle mass)
balance of nitrogen in the body
- intake from protein in the diet
- goes into amino acid pool and can then be used for body protein or made into urea and excreted
- if you are in a positive balance you will have more going to body protein than you are excreting
- during times of insufficient protein, you have more going back into the amino acid pool from the body protein and that is being made into urea
tramua and urea balance
- high energy requirement
- a lot more going into the amino acid pool and being made into urea
what are the 3 steps of removin nitrogen
- transfer to a common carrier
- ammonia is regenerated in the liver
- ammonia is incoporated into urea
what is a common carrier of nitrogen
-alpha ketogluterate which then turns into glutamate
PLP
- is used by aminotransferase in order to transfer a nitrogen from an amino acid a common carrier
- arises from VB6
- exhanges a keto group fro a amine group
glutamate dehydrogenase
- location
- function
- what happens to its product in the liver
- cofactors
- this is located in the mitochondria and is fundamental for the release of ammonia so it can be acted on by CPSI to create carbamoyl phsophate for the urea cycle
- in liver, the ammonia produced can be incorporated into urea
- urea production is significant only in the liver
- uses NAD or NADP as cofactors
regulation of glutamate dehydrogenase
- activity increased by ADP and GDP
- activity decreased by ATP and GTP
what is ammonia produced from on asparagine and glutamine
-amide groups
minor way to dispose of ammonia
- make glutamate by running the glutamate dehydrogenase reaction in reverse
- this is when the urea cycle is saturated
major way of disposing of ammonia
- make glutamine via the glutamine synthase reaction
- used to fix ammonia especially in the brain; also occurs in muscle, lungs, and adipose tissue
- glutamine is a majr carrier of n in the blood
- glutamine levels increase after a protein rich meal
problem with hyperammonemia in children
- glutamate can only hold so much ammonia as glutamine before it maxes out and the body runs out of glutamine
- when this happens, hyperammonemia will present and this can cause serious health problem (especially in the brain)
urea cycle order and mnemonic
- ordinarily careless crappers are also frivolous about urination
- ornithing, carbamoyl phosphate, citrulline, aspartate, arginosuccinate, fumarate, arginine, urea
CPSI
- founds in the mitochondria
- needs NAG to function
- NAG is made by NAG synthase using acetyl-CoA and glutamate
- NAG synthase uses arginine
- produces carbamoyl phosphate from NH4 which comes from the glutaminase and glutamate DH reactions
how is Nag synthase deficiency treated?
with carbamoyl glutamate
what does a deficiency in any of the urea cycle enymes result in?
-elevated ammonia
where do the two nitrogens that make up urea come from?
aspartate and NH4 from carbamoyl phosphate
how many ATPs are used to make urea
4
clinical symptoms of a inoperative or stressed urea cycle -
- developmental delays
- cognitive delays
- seizure
- protein intolerance
diagnosing urea cycle defs
- blood/urine amino acids analyses for ammonia
- enzyme assay
treatment of yrea cycle disorders
- restrict proteins from diet, this lowers nitrogen production
- supplement with arginine
- increase nitrogen excretion using benzoate or pheylacetate or phenylbutyrate
how does the urea cycle interact with carb metabolism
- argininosuccinate is converted into fumerate using argininosuccinase
- fumerate can then be converted into OAA for gluconeogenesis, or into malate for pyruvate/PEP or sent to the mitochondria to directly aparticipate in the TCA
why might we need to replenish ornithine or arginine and how do we do so
-ornithin can be used to make polyamine (spermine)
-arginine is used to make NO which is a vasodilator
-glutamine can be used to make glutamic semialdehyde which can be converted into ornithine
glutamic semialdehyde can also be made from ornithine which can then be used to make proline
