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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.

Pathway

Purine degradation & uric acid · Cytosol (nucleotidase, PNP, ADA) and liver/gut xanthine oxidase; uric acid excreted by the kidney. Enzymes sit beside the arrows; a ★ marks the rate-limiting step. The map scrolls inside its panel.

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Purine degradation & uric acid

Xanthine

Made from Guanine by Guanine deaminase

Guanine deaminase — Purine degradation & uric acid

Releases NH₃.

Made from Hypoxanthine by 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 →

Becomes Uric acid (urine) via Xanthine oxidase ★

Xanthine oxidase ★ rate-limiting — Purine degradation & uric acid

Cofactors: O₂ → H₂O₂

Inhibited by: Allopurinol; Febuxostat

Uric acid is the final purine product in humans; serum saturation ≈ 6.5 mg/dL.

Condition cards:Gout →Allopurinol →