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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

Catecholamines, serotonin & the tyrosine tree · CNS and sympathetic ganglia (dopamine, NE); adrenal medulla only for epinephrine; melanocytes for melanin; liver for the degradation arm; serotonin in CNS raphe nuclei, gut enterochromaffin cells and platelets, with melatonin made from it in the pineal. Enzymes sit beside the arrows, ★ = rate-limiting, ⊕/⊖ = activators/inhibitors (toggle), −ATP +NADH = what the step spends and makes (toggle ⚡), dashed = allosteric signal, shaded bands = compartment. Drag to pan.

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Catecholamines, serotonin & the tyrosine tree

4-Hydroxyphenylpyruvate

Made from TYROSINE — the branch point by Tyrosine aminotransferase

Tyrosine aminotransferase — Catecholamines, serotonin & the tyrosine tree

Cofactors: PLP (vitamin B₆)

Deficiency: Tyrosinemia type II (oculocutaneous) — corneal and skin lesions from tyrosine crystals

The catabolic route, in liver.

Becomes Homogentisic acid via 4-Hydroxyphenylpyruvate dioxygenase

4-Hydroxyphenylpyruvate dioxygenase — Catecholamines, serotonin & the tyrosine tree

Cofactors: Vitamin C (ascorbate)

Deficiency: Tyrosinemia type III — rare, neurologic

This is the enzyme NITISINONE blocks on purpose, to treat tyrosinemia type I — you stop the pathway ABOVE the toxic metabolite and accept a high tyrosine instead.