How do oxidative deamination and transamination differ? What are the main enzymes for each (1,2)
Oxidative deamination releases amino group as free NH3, whereas transamination transfers it.
Oxidative deamination: glutamate dehydrogenase
Transamination: ALT and AST
Where does oxidative deamination mainly take place? How about transamination?
Oxidative deamination mainly takes place in liver & kidney
Transamination: liver, muscle.
How do transamination and oxidative deamination work together?
Amino groups of most AA are ultimately funneled to glutamate via transamination with a-ketoglutarate.
Glutamate is then deaminated by glutamate dehydrogenase to release free ammonia (regenerating a-ketoglutarate) for C skeleton.
Does glutamate dehydrogenase use NAD+ or NADP+ as a coenzyme?
Can actually use both. NAD+ is usually used in oxidative deamination (simultaneous loss of NH3 + oxidation of carbon skeleton), while NADP+ is used in reductive amination (sim gain of NH3 + reduction of C skeleton).
What allosterically activates and inhibits glutamate dehydrogenase? (2 each)
What does glutamate DH do during starvation? After protein-rich meal?
ADP & GDP activate; ATP & GTP inhibit.
Starvation: low cellular energy, need high AA degradation to get energy production --> increased synthesis of a-ketoglutarate for TCA
Protein rich: Also need GDH for degradation and ammonia production for excretion.
Why are NH3 levels highly regulated?
Bc hyperammonemia is highly toxic to brain.
How is free ammonia transferred from tissues to liver?
What enzyme? What does it require? What is the transporter?
1. Glutamine synthetase (many tissues) adds free ammonium to glutamate --> glutamine; requires ATP (serves as non-toxic ammonia transporter).
How many ammonia groups does glutamine carry?
What happens to glutamine in (1) liver and (2) kidney?