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.
Purine degradation & uric acid
Hypoxanthine
Made from Inosine by Purine nucleoside phosphorylase (PNP)
Purine nucleoside phosphorylase (PNP) — Purine degradation & uric acid
Cofactors: Pi → ribose-1-P
Deficiency: PNP deficiency — milder, predominantly T-cell immunodeficiency (B cells relatively spared); supportive care / transplant
Condition cards:Purine nucleoside phosphorylase (PNP) deficiency →
Becomes Xanthine via Xanthine oxidase
Xanthine oxidase — Purine degradation & uric acid
Cofactors: O₂ → H₂O₂
Inhibited by: Allopurinol (hypoxanthine analog); Febuxostat
Allopurinol blocks both xanthine oxidase steps; the more soluble hypoxanthine and xanthine are excreted instead. Allopurinol also raises 6-MP levels (same enzyme degrades it).
Condition cards:Gout →Allopurinol →