Amino Acid Metabolism Flashcards
What are the sources of amino acids?
- Degradation of ingested protein
- Degradation of synthesized endogenous protein
- AA biosynthesis
What are the free amino acids used for?
- Make purines/pyrimidines
- Make glucose
- Make ketones
- Degraded into nitrogen for release as urea
What enzymes are the most rapidly degraded?
Proteins most rapidly degraded are often ones
of the rate limiting step
What is nitrogen balance?
It is the intake and excretion of nitrogen and should be 0 in normal people.
When does positive nitrogen balance occur?
Pregnancy
Growth
Bodybuilding
When does negative nitrogen balance occur?
Starvation
Cancer
Trauma
What is the general pathway for urea formation from amino acid degradation?
Free amines -> Glutamate -> Ammonia OR Aspartate -> Urea
Where is urea synthesized?
Liver
What is the transamination reaction?
It is the transfer of the amine group on an amino acid to α-ketoglutarate which then generates glutamate
What is the cofactor necessary for the transaminase enzymes to carry out transamination?
Pyridoxal Phosphate
What serves as the nitrogen reservoir in the body?
Glutamate
What do elevated levels of Alanine transaminase and/or Aspartate transaminase indicate?
They indicate liver tissue damage as the hepatocytes are lysing.
How is glutamate converted to aspartate?
Aspartate Transaminase
How is glutamate converted to ammonia?
Glutamate Dehydrogenase
What is the primary regulated step of urea synthesis?
Formation of carbamoyl phosphate
What is the enzyme that catalyzes the regulated step of urea synthesis?
Carbamoyl phosphate synthetase I
What is the allosteric activator of carbamoyl phosphate synthetase I?
N-acetylglutamate
What enzyme converts arginine into urea?
Arginase
Within the cell, where does the conversion of NH3 to carbomoyl phosphate and conversion to citrulline occur?
In the mitochondria. The rest of the urea cycle reactions occur in the cytosol.
What can occur with hyperammonemia?
Hepatic coma
What are glucogenic amino acids?
They can be converted to TCA cycle intermediates
or pyruvate for gluconeogensis
What are ketogenic amino acids?
They can be converted to acetyl CoA, acetoacetyl CoA, or acetoacetate
Name the ketogenic amino acids.
Lysine
Leucine
What occurs to amino acid and protein synthesis after a meal?
Protein synthesis will increase under the effect of insulin
What occurs to protein synthesis during an overnight fast?
Protein synthesis will be inhibited, with glucagon promoting protein degradation
