Nitrogen Metabolism Flashcards
Is there any nitrogen storage in the body?
NO
Nitrogen balance-3 possibilities
- Balanced: normal adult
- Positive: increase in protein synthesis (normal in children)
- Negative: Catabolic response to trauma/starvation
Trauma leads to stress hormones-mobilization of carbon skeletons
What are the Essential Amino Acids?
Arginine
Leucine
Histidine
Isoleucine
Tryptophan
Threonine
Methionine
Phenylalanine
Valine
“A Little Humility In Learning Ten Tiny Molecules Proves Valuable”
Ketogenic Amino Acids
Yields:
* Acetoacetate
* Acetyl CoA
* Acetoacetyl Coa
Leucine, Lysine
“Losers”
Both Glucogenic and Ketogenic
Threonine
Tyrosine
Tryptophan
Isoleucine
Phenyalanine
“TTTIP”
Glucogenic Amino Acids
Glycine
Serine
Glutamate
Not comprehensive
What is the process of removing an amino group?
Transaminiation
Products are:
1. Alpha Ketoglutarate
2. Glutamate
What are the two amino acids that do not participate in transamination?
- Threonine
- Lysine
Alanine aminotransferase (ALT)
Also called: Glutamate-pyruvate transaminase (GPT)
* present in liver in highest concentrations
* readily reversible
* glutamate acts as a collector of nitrogen from alanine
Aspartate aminotransferase (AST)
Also called: Glutamate-oxaloacetate transaminase (GOT)
* Found in a variety of tissues
* Forms aspartate which is used a nitrogen source in the urea cycle
Oxidative deamination pathway
- Liberates ammonia and a-keto acid (liver and kidney)
- Glutamate dehydrogenase (mitochondrial)
What are the 7 products from the breakdown of C-skeleton of amino acids
- Oxaloacetate
- a-ketoglutarate
- Pyruvate
- Fumarate
- Succinyl CoA
- Acetoacetyl CoA
- Acetyl CoA
Where is urea produced?
In the liver and transported in urea to the kidney for excretion in urin
Where are the two nitrogens in the urea cycle from?
Both from glutamate
1. Transamination
2. Oxidative deamination
Where is arginase found in the body?
ONLY IN THE LIVER
How many ATP does it take for 1 molecule of NH3?
3 ATP
Regulation of the Urea Cycle
- N-acetyl glutamate: essential allosteric activator of CPS I (RLS in mitochondria)
- Increases after ingestion of protein-rich meal (glutamate/arginine)
What are the 6 sources of ammonium?
- Amino Acids-produced in many tissues
- Glutamine via renal glutaminase-important for acid-base balance
- Glutamine via intestinal mucosal cells
- Bacterial action in intestine breakdown urea in the intestine to ammonia
- Amines breakdown of neurotransmitters
- Purines/Pyrimidines Catabolism of amino groups
Transport of ammonia in circulation (2)
- Urea: Most important transport system of ammonia. Transported from liver to kidney
- Glutamine: non-toxic storage and transport of NH3. Mostly in muscle and liver
Acquired hyperammonemia: Alcoholism/Hepatitis/Biliary obstruction
May cause collateral circulation around liver
Acquired hyperammonemia: Reye’s Syndrome
- Occurs primarily in children w/ chickenpox or influenza AND given salicylates
- Leads to mitochondrial damage and disruption of urea cycle
- High levels of serum transaminase
Hereditary hyperammonemia (1 in 30,000 births)
Genetic deficiency of any 1/6 of the urea cycle enzyes
* Results in mental retardation
* Death soon after birth
Urea Cycle Overview
