Amino Acids/Urea Cycle Flashcards
Name an alpha keto acid used in muscle metabolism in aerobic conditions:
Pyruvate! (alpha keto acid of deaminated Alanine)
How do amino acids get oxidized and where does this process take place?
AA lose their amino groups (NH3+) to form alpha keto acids which can be further oxidized to produce energy
In the liver cytosol!
What are the enzymes responsible for catalyzing transaminations?
Aminotransferases
How does the muscle deliver excess amines as ammonia ions to the liver for processing?
Alanine (which is transaminated to pyruvate)
Which amino acid contains 2 amine groups in its structure, Q or E?
Q = Glutamine
If Glutamine gives up 1 of its amine groups, what does it become? Where does the second amine group go?
Glutamate
Urea (as ammonium)
What does glutamate indicate about our nitrogen metabolism?
Indicates intracellular levels of amine groups captured as NH4
What does glutamine indicate about our nitrogen metabolism?
Indicates the extracellular levels of amine groups because the other tissues are getting rid of their excess amines as glutamine (excess amines collected from kidneys and intestines processed in the liver as glutamine and are excreted as urea)
Which of the following amino acid metabolites is synthesized in the liver cytosol? A) Glutamine B) Alpha-KG C) Glutamate D) Glutamate dehydrogenase
C) Glutamate! Forms when an amino acid donates an amine group to alpha-KG
Where in the liver cell does glutamate give up its amino group? Where does glutamine give up its amino group? Who are they giving it to?
Glutamate will enter the mitochondria and associate with glutamate DHase and in the process it will give up the amino group to form NH4
Glutamine will enter the mitochondria and will give up its amine groups to alpha ketoglutarate to form glutamate and subsequently associate with glutamate DHase
Where are amino groups from amino acids transferred to alpha ketoglutarate?
Liver cytosol
What cofactors are needed for transamination to occur? Would this be a prostethic group?
PLP (pyridoxal phosphate) co-factor
**Prostethic group b/c PLP is covalently bound to the aminotransferases active site through a Lys residue
What does the aldehyde form of PLP do?
Forms and accepts the amino group
What does the aminated form of PLP do?
Donates the amino group
What are the 2 fates of amino acids that are processed in the liver?
1) Resulting alpha-keto acids can be further oxidized (i.e. pyruvate –> TCA –> ATP)
2) Eliminate NH4 as urea
Which enzyme cataylzes oxidative deamination in the liver mitochondria?
Glutamate Dehydrogenase = reduces NAD+ to oxidize glutamate into alpha-ketoglutarate
What are 3 products released from glutamate dehydrogenase?
1) alpha-KG
2) NH4+
3) NADH + H+
How does glutamine transport NH4+ into the bloodstream?
NH4+ produced in the extrahepatic tissues is transported in the blood as glutamine
Glutamine is formed from Glu + NH4+ = Gln
via glutamine synthetase
Why does glutamine synthetase utilize ATP in its catalytic mechanism?
Adenylylation
1) Adds an excellent leaving group (phosphoryl)
2) Enhances the electrophilicty of the carbonyl carbon on glutamate for NH4+ (nucleophile)
What are the 2 fates of Gln entering the liver for processing?
1) Loses an amine group to become Glutamate (via aminotransferase) and another to form urea
2) Gln can transfer its alpha amino group to pyruvate to generate alanine
Where are the 2 amino groups of urea coming from? Who donates them?
1) Carbamoyl phosphate
2) Aspartate
For every 1 molecule of urea how many amine equivalents are leaving the body?
2!
Which metabolites function in the “shunt” between urea cycle and TCA cycle?
Fumarate and OAA
Which TCA cycle metabolite is produced as a byproduct of the urea cycle?
Fumarate
