Activated by ADP and GDP allosterically (low energy)
Inhibited by ATP and GTP
Also depends on concentrations of rxns and products: relative concentrations of glutamate:a-ketoglutarate, ammonia, and oxidized to reduced coenzymes.
What direction does glutamate dehydrogenase rxn strongly go towards?
Goes strongly towards production of a-ketoglutarate and free NH3 (catabolism)
What are the effects of high-protein meal vs starvation?
Which will have AA degradation? Ammonia formation? AA synthesis?
What is the effect of increased protein on glutamate production for ALT?
Starvation --> low ATP:ADP and low GTP:GDP, so need high AA degradation to get energy production from C skeletons, thus increased synthesis of a-ketoglutarate for TCA cycle or for GNG.
Also get amino acid degradation and ammonia production. In liver, rxn proceeds in direction of AA degradation and formation of ammonia to get rid of excess protein. BUT CAN ALSO GET AA SYNTHESIS FROM CORRESPONDING A-KETO ACIDS.
Increased protein --> increased glutamate
How is NH3 transported to liver/kidney (2) (most tissues vs. ? Why are NH3 levels so highly regulated? (3)
In most tissues: glutamate + NH3 + ATP -- glutamine synthetase --> glutamine (nontoxic transport form of 2 ammonias) --> liver.
Muscle (glucose alanine cycle):
Transamination of pyruvate to form alanine. Alanine is transported to liver via blood and is converted to pyruvate and glutamate --> GNG.
What is the main purpose of urea cycle? How many ATP does it require? Where do its 2 nitrogens (Ns) come from (which compounds) and what do they combine with?
Main purpose: major route for NH3 disposal.
ATP - 3
2 Ns: NH3 (oxidative deamination) and from aspartate combine with CO2.
What does BUN stand for? When will it be high? What can it measure?
BUN = blood urea nitrogen
Will be high with faulty urea synthesis (faulty waste disposal).
Measures nitrogen balance
What is the mechanism of urea synthesis pathway?
How is urea cycle regulated? (4)
Activated by high protein diet, high protein meal containing arginine, N-acetylglutamate, and starvation.
1. Long-term: Activated by high protein diet (increased use of protein for energy/catabolism --> increased urea) also activated by starvation (use of body protein as energy) upregulates autophagy and expression of urea cycle enzymes.