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.
Methionine cycle & homocysteine's two fates
Succinyl-CoA → TCA cycle
Made from Propionyl-CoA by Propionyl-CoA carboxylase → methylmalonyl-CoA mutase
Propionyl-CoA carboxylase → methylmalonyl-CoA mutase — Methionine cycle & homocysteine's two fates
Cofactors: Biotin (B₇), Adenosylcobalamin (B₁₂)
Deficiency: Methylmalonic acidemia (mutase deficiency or B12 deficiency) — methylmalonic acid accumulates
This is the SECOND of the two B12-dependent reactions in the body — the other is methionine synthase on the other arm of this same fork. It is also where methylmalonic acid comes from, which makes it the lab discriminator: folate or B12 deficiency both raise homocysteine, but ONLY B12 deficiency also raises methylmalonic acid.