Amino Acid Metabolism Flashcards
What are nitrogen assimilation and nitrogen fixation and how are they different? Which is more costly?
2 ways for nitrogen to enter biosphere
Fixation most costly and difficult, assimilation = predominant strategy
What enzymes and substrates bring nitrogen into the biosphere?
Fixation: nitrogenase + reductase
Assimilation: glutamate dehydrogenase (GDH) + glutamine synthetase + glutamate synthase
What are the reactants and products of a transaminase reaction?
amino acid and keto acid
Alpha ketoacid
Deaminated form of AAs
What cofactor is involved in transamination reactions?
pyridoxal phosphate (Vitamin B6)
Why are transaminases important—what role do they play in amino acid metabolism?
Transferring the amino group from abundant AA (glutamate) to an alpha ketoacid acceptor, creating a new AA
Why is vitamin B6 important? What would be some consequences of B6 deficiency?
B6 deficiency causes changes in carbon skeleton of AAs, makes AA essential
Symptoms: skin rashes, mental changes
What makes an amino acid essential?
Not made by the body (not via metabolic intermediates), comes from dietary source
Limiting amino acid
AA present in lowest amount in body
When runs out, synthesis of any proteins that require it will stop
Limits how much protein can be synthesized
Why are some amino acids considered “conditionally essential”?
AAs usually not essential, except in times of illness and stress
Why are proteins broken down in starvation– what are they used for?
Fuel source (glucose)
What are the major carriers of carbons derived from protein degradation to liver for gluconeogenesis?
ammonium, pyruvate
How is the NH4+ removed and where does this occur?
Removed in mitochondria by glutaminase
What is the glucose-alanine shuttle?
Purpose: transports nitrogen in a non-toxic form from peripheral tissues to the liver
Steps:
- Protein from muscle degraded for fuel
- Ammonium stripped from glutamate and then to alanine
- Alanine carries ammonium to liver
- Transferred back to glutamate and then detoxified in urea cycle
- Pyruvate generated by aminotransferase rxn used for gluconeogenesis
What’s the role of the Urea cycle? When is it active? What turns it on?
Eliminates toxic ammonium from the body
Active after a high protein meal and during a states of starvation
Turned on by N-acetyl-glutamate (a required allosteric activator)
