Learn / Metabolism
Metabolic pathways
Every FMK pathway as a clickable map. Pick one pathway to hammer it — next step, enzyme, regulator, cofactor, and the facts that get tested (NADPH and who needs it, rate-limiting steps, deficiencies) — or set it to all pathways for a mixed drill. Every answer says which enzyme and which pathway.
Nitrogen transport to the liver — Cahill cycle & the glutamine shuttle
NH₄⁺ in the hepatocyte mitochondrion
Made from GLUTAMINE — carries TWO nitrogens by GLUTAMINASE (liver)
GLUTAMINASE (liver) — Nitrogen transport to the liver — Cahill cycle & the glutamine shuttle
Releases the ammonia for disposal, right where the urea cycle can use it.
Made from Glutamate (liver) by GLUTAMATE DEHYDROGENASE (GDH) — oxidative deamination
GLUTAMATE DEHYDROGENASE (GDH) — oxidative deamination — Nitrogen transport to the liver — Cahill cycle & the glutamine shuttle
Cofactors: NAD(P)⁺ → NAD(P)H
Deficiency: Liver failure — GDH activity and overall ammonia handling fall, which is one of the converging reasons cirrhotic patients develop hepatic encephalopathy
The step that finally releases FREE ammonia, in liver and kidney mitochondria. Glutamate is oxidised to α-ketoglutarate and NH₄⁺ (s9).
Becomes → UREA CYCLE via Into CPS-I — the urea cycle begins
Into CPS-I — the urea cycle begins · irreversible — Nitrogen transport to the liver — Cahill cycle & the glutamine shuttle
See the urea cycle map: this ammonia becomes the FIRST of urea's two nitrogens.