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nitrogen compoounds are degraded into mostly

-urea levels are the only thing that changes in excretion with regards to proteins intake


excretion in urine comes in four forms

-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



-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
-what happens to its product in the liver

-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



-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



clinical symptoms of a inoperative or stressed urea cycle -

-developmental delays
-cognitive delays
-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