Category: biosynthesis
Most-abundant free amino acid in mammals; not protein-bound. Synthesized from cysteine: cysteine → cysteine sulfinic acid (via cysteine dioxygenase, CDO1) → hypotaurine (via cysteine sulfinic acid decarboxylase, CSAD, the rate-limiting step) → taurine (via hypotaurine dehydrogenase). Major uses: (1) bile-acid conjugation (cholic + chenodeoxycholic acid + taurine → taurocholate / taurochenodeoxycholate, ratio 1:3 with glycine conjugates in humans); (2) osmolyte in retinal photoreceptors + cardiomyocytes; (3) GABA-A receptor agonist (CNS inhibition); (4) cardioprotection (taurine deficiency in cats → dilated cardiomyopathy, a classic veterinary observation that drove discovery of taurine essentiality in cats). Humans can synthesize but at low rates — supplemental taurine is investigated for CHF, post-MI cardioprotection, and as a popular component of energy drinks (proposed efferent + glycemic effects).