Abstract
Evidence that taurine synthesis may occur in the brain was provided by the finding that brain cortex slices produced labelled taurine after incubation with [35S]methionine or [35S]cysteine (39). Radioactive taurine was also found in the brain after intracisternal injection of radiolabelled cysteine (11). Cysteine sulfinate was found as an endogenous compound (3,4) or as a labelled precursor of taurine (36) in brain tissue while cysteamine or cystamine could not be detected (23). Accordingly, biosynthesis of taurine in the brain is thought to occur from cysteine through the so-called cysteine sulfinate pathway; i.e. oxidation of the thiol group of cysteine to form cysteine sulfinic acid, followed by decarboxylation to hypotaurine and subsequent oxidation to taurine. Cysteine sulfinate might be also first oxidized to cysteic acid followed by decarboxylation directly to taurine. In the liver, where this pathway was first demonstrated (22), decarboxylation of both cysteine sulfinate and cysteate was shown to be performed by the same enzyme, called cysteine sulfinate decarboxylase (E.C.4.1.1.29) rather than cysteate decarboxylase since it has a better affinity for cysteine sulfinate than for cysteate (21). In vivo, cysteine sulfinate decarboxylase was suggested to be the rate-limiting enzyme for taurine biosynthesis in liver (14).
Published Version
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