Amino Acid Metabolism - German Flashcards
What are the 4 fates of dietary amino acids?
Protein synthesis
Energy production (CAC)
Biosynthesis
Urea excretion
What happens to excess dietary amino acids?
No storage occurs - if not used, it is excreted
What are the 3 drivers of protein oxidation?
Normal synthesis and degradation
Protein rich diet
Starvation or diabetes mellitus
Pepsinogen is cleaved into what by what?
Pepsin - HCl
Strictly ketogenic or both keto/gluco AA’s. Lucy lies (and) Tyrone try’s (to) fence three isolated (guys).
Lucy - Keto Lies - Keto (and) Tyrone Try’s (to) Fence Three Isolated (guys)
What is pepsin?
A protease
What does pepsin hydrolyze?
Phe, Trp, Tyr polypeptide bonds
What does secretin stimulate and from where?
Release of bicarb from pancreas
What does CCK stimulate and from where?
Zymogen release from pancreas
Name 3 pancreatic zymogens and what they are cleaved into.
Trypsinogen - Trypsin
Chymotrypsinogen - Chymotrypsin
Procarboxypeptidase A and B - Carboxypeptidase A and B (Breakdown peptides further)
What is a zymogen?
Enzyme precursor that requires a biochemical change for activation, typically cleavage
What are three fates of amino acids?
Used for protein and biosynthesis w/in cells
Catabolized for energy w/in cells
Transported to the liver and excreted
What are the 4 amine group carriers, precursors and common metabolites, and entry and exit molecules from the CAC?
Glutamate
Aspartate
Glutamine
Alanine
Alanine from where is fed into the liver?
Muscle
Glutamine from where is fed into the liver?
Muscle and other tissues
How are other aa’s introduced into the liver?
AA’s from ingested protein enters the liver
Why is ammonia toxic?
It can cross the BBB.
It disrupts K+ uptake, and high extracellular K+ prevents GABA inhibition (this shuts down the nervous system)
Humans excrete excess ammonia as what?
Urea
What are the essential AA’s?
P - Phe V - Val T - Trypto T - Threo M - Met H - His I - Iso L - Leu L - Lys
What are the nonessential AA’s?
Alan - Alanine Ate - Asparagine Asparagus - Aspartate Gliding - Glutamate South - Serine
What are the conditionally essential AA’s?
Argyle - Arginine Can - Cysteine Get - Glycine Gutta - Glutamine Percha - Proline Tomorrow - Tyrosine
What are two common amino acid catabolism rxns?
Transaminase rxns
One-carbon transfers
What is the point of the transaminase rxn?
To remove or add NH3 groups from AA’s.
Why add? To synthesize other AA’s
What is the common coenzyme in transaminase rxns?
Pyridoxal Phosphate (PLP) [Amino-transferase]
**This is a carrier of amino groups
Removal of NH3 group goes from what to what?
Amino acid to alpha keto acid
How is intracellular ammonia buffered?
Converting glutamate to glutamine
Most cells have what that takes ammonia and glutamate to make glutamine intracellularly?
Glutamine synthetase
Tell me 3 things that the glutamine-alanine cycle does.
Allows proteins to function as energy sources
Occurs in anaerobic states
Coincides with the cori cycle
Tell me what happens to glutamine in the urea cycle.
It is converted to glutamate via glutaminase
Amino acids and alanine (from muscle) are converted to _____________ via a transaminase rxn with the enzyme ___________. Then, it is turned into ___________ via a one-carbon transfer. Then, via a transaminase rxn, it is turned into _____________.
Alpha-keto acid
PLP
Alpha-ketoglutarate
Glutamate
Once inside the mito matrix of a hepatocyte, glutamate is turned into what? Hint: 1 of 2 things.
Either NH4+ or alpha-ketoglutarate.
As the glutamate to alpha-ketoglutarate rxn occurs, oxaloacetate is turned into _______________ via _____________.
Aspartate
Aspartate aminotransferase
What happens to the aspartate?
It is transported out and thrown into the urea cycle in the making of argininosuccinate from citrulline.
NH4+ is made from glutamate via ____________.
Glutamate dehydrogenase
The NH4+ in the matrix is turned into ___________ via ______________.
Carbamoyl phosphate
Carbamoyl phosphate synthetase I.
What are the substrates of the urea cycle in order and which ones share a transporter into and out of the liver cell?
Citrulline (T-porter out of the cell) Citrullyl-AMP intermediate Argininosuccinate Arginine (Urea is a by-product of this rxn [Arginine to Ornithine]) Ornithine (T-porter into the cell)
What part of the urea cycle happens in the mitochondrial matrix?
Ornithine to citrulline with carbamoyl phosphate feeding in. From citrulline on, it happens in the cytosol.
Of the urea produced in the liver 75% goes where and 25% goes where?
Urinary excretion as urea
Into bile which empties into duodenum
*Some of the 25% is pooped out, while some of is recycled back. 85% of the recycled goes thru the portal circulation back to the liver while 15% goes into the systemic circulation to tissues for protein synthesis
What are two ways that the urea cycle is regulated?
Increased synthesis of urea cycle enzymes
Allosteric carbmoyl phosphate synthetase I
What is the linker b/t the urea cycle and the malate-aspartate shuttle/CAC?
Arginine-succinate which is called the aspartate-argininosuccinate shunt of CAC
Those amino acids that feed into acetyl-CoA, Pyruvate, and alpha-ketoglutarate are _____________ in energy producing compared to those that input at other levels in the CAC.
HIGHER
What does glucogenic mean? What does ketogenic mean?
AA’s that can be converted to glucose
AA’s that can be converted to ketone bodies
What are the 3 important one carbon transfer rxn cofactors?
BIOTIN
Tetrahydrofolate (H4 folate)
S-Adenosylmethionine (adoMet)
6 AA’s are degraded to pyruvate. Name them. G3 CASTry
Gly Threo Cys Ala Ser Try
Py - *G3 CASTry
7 AA’s are degraded to Acetyl-CoA. Name them. Try 3T PILL
Try Threo Tyro Phe Iso Leu Lys
*Ace - Try 3T PILL
5 AA’s are degraded to alpha-ketoglutarate. Name them. Alpha - 2 Glu PAH
Glutamate Glutamine Proline Arginine Histidine
*Alpha - Glu 2 PAH
4 AA’s are degraded to succinylcholine-CoA. Name them. Succ - 3M IV.
Met
Iso
Val
Threo
*Succ - 3M IV
2 AA’s are degraded to oxaloacetate. Name them. Oxalo loves 2 asparagus.
Asparagine
Aspartate
*Oxalo loves 2 asparagus
What is the rate limiting step of the urea cycle?
The formation of carbamoyl phosphate from ammonium + the concentration of orthinine
