Metabolic Fates of Amino Acids Flashcards
What are the components bound to the α-carbon in an amino acid structure?
The α-carbon is bound to:
An amino group (NH3+/NH2)
A carboxyl group (COOH/COO-)
A hydrogen atom
An R-group (side chain)
What are the primary metabolic fates of amino acids in mammals?
The amino group is metabolized to urea (or uric acid in birds).
The carbon skeletons are converted into intermediates of the citric acid cycle
The amino group is metabolized to urea (or uric acid in birds).
The carbon skeletons are converted into intermediates of the citric acid cycle.
Flashcard 3: Amino Group Transport
Q: Why is the transport of nitrogen (amino groups) crucial in amino acid metabolism?
The transport of nitrogen is essential to:
Facilitate the synthesis of urea for excretion.
Provide amino groups for energy intermediate production to generate ATP.
What is transamination, and what does it achieve?
What is transamination, and what does it achieve?
A: Transamination is the enzymatic transfer of an amino group from an α-amino acid to an α-keto acid. It:
Collects amino groups from various amino acids as L-glutamate.
Utilizes α-ketoglutarate as the primary amino group acceptor.
Is catalyzed by aminotransferases.
What role does Pyridoxal Phosphate (PLP) play in transamination reactions?
PLP is a prosthetic group derived from vitamin B6.
It serves as an amino group carrier in a “ping-pong” reaction mechanism.
PLP alternates between pyridoxal phosphate (accepting amino groups) and pyridoxamine phosphate (donating amino groups).
Describe the “ping-pong” mechanism of transamination
One substrate binds, and the first product is released.
The enzyme is modified to an intermediate form.
The second substrate binds, leading to the formation and release of the second product.
How are amino groups from dietary protein metabolized?
Dietary amino acids are transported to the liver via the circulatory system.
In hepatocytes, amino groups are transferred to α-ketoglutarate, forming glutamate.
Glutamate enters mitochondria and releases NH4+.
How is free ammonium (NH4+) metabolized in extrahepatic tissues?
Free NH4+ is toxic and converted to glutamine by glutamine synthetase (requires ATP).
Glutamine transports NH4+ to the liver, where glutaminase releases NH4+ and regenerates glutamate.
How are amino groups metabolized in vigorously contracting skeletal muscle?
Muscle produces pyruvate (via glycolysis) and NH4+ (via protein catabolism).
Pyruvate is transaminated to alanine, which is transported to the liver.
In the liver, alanine transfers NH4+ to α-ketoglutarate, forming glutamate and pyruvate
What is the glucose-alanine cycle?
In muscle: Alanine aminotransferase transfers NH4+ from glutamate to pyruvate, forming alanine.
Alanine is transported to the liver.
In the liver: Alanine aminotransferase transfers NH4+ from alanine to α-ketoglutarate, regenerating pyruvate and glutamate.
Pyruvate enters gluconeogenesis to produce glucose.
What is oxidative deamination, and how does it contribute to amino acid metabolism?
Oxidative deamination removes the amino group from L-glutamate.
Catalyzed by L-glutamate dehydrogenase.
Produces NH4+, α-ketoglutarate (a citric acid cycle intermediate), and NAD(P)H.
What is transdeamination, and what reactions does it combine?
Combines transamination (amino group transfer) and oxidative deamination (amino group removal).
Results in the production of NH4+ and a-keto acids from amino acids.
What happens to glutamate in liver mitochondria during amino acid catabolism?
Glutamate transports amino groups into mitochondria.
Undergoes oxidative deamination to release NH4+ and regenerate α-ketoglutarate.
How are alanine and aspartate aminotransferase levels in blood clinically significant?
Elevated levels indicate liver damage from infection, alcohol consumption, or drug toxicity.
These enzymes are abundant due to their roles in the glucose-alanine cycle and urea production.
