Cysteinesulphinic acid

Incubation of embrionic calf liver with 35S-labelled sodium sulphite, sodium pyruvate and sodium glutamate at 38 °C under nitrogen resulted in formation of 35S-cysteinesulphinic acid133,134. 35S-hypotaurine has also been isolated, but taurine-35S and cystine-35S have not been found. In the presence of serine, the yield of 35S-cysteinesulphinic acid was smaller. Organic 35S compounds without amino groups have also been formed in the same experiment. In the conditions employed in this bioexperiment cysteinesulphinic acid is not reduced to cystine-3 5S, although such reduction was found possible in vivo. 

The [3 5S] cysteinesulphinic acid, included in the scheme in equation 81, has been identified unambiguously by Chapeville and Fromageot149 in the liver and kidney of seven-week-old rats injected with [35S]cystine hydrochloride and sacrified 15 minutes later. [35S]Taurine and [35S]sulphate have also been detected, and the [35S]cysteinesulphinic acid has been oxidized subsequently by performic acid to [35S]cysteic acid. 

The aerobic metabolism of cystine-3 5S by chicken embryo, investigated166 both in vivo and in vitro, resulted in the formation of cystinedisulphoxide-35S (in vitro only), [35S] cystinesulphinic acid, [35S] cysteic acid, [35S]taurine and sulphate-35S. Hypotaurine has been detected neither in vivo nor in vitro. This indicates that, contrary to what had been observed in mammalian liver, hypotaurine is not the precursor of taurine in chicken embryo (equation 86). The enzyme decarboxylase, which effectively decarboxylates [35S]cysteic acid, does not act on cysteinesulphinic acid. Sulphate-35S may be produced also by the desulphination of cysteinesulphinic acid (equation 87) or from some other... 

Enzymic decarboxylations of [1 -uC]cysteinesulphinic acid and /I -uC]cysteic acid in mammalian tissues... 

The metabolism of 35S-labelled sulphur amino acids in marine and fresh water invertebrates has been studied and reviewed by Awapara and coworkers179 180. The general conclusion drawn from these studies was that the metabolism of sulphur-bearing amino acids in two molluscs studied is qualitatively the same as in mammals. Taurine, which serves as an osmoregulator in marine molluscs, is formed either by decarboxylation of cysteic acid (in Rangia cuneata) or by oxidation of hypotaurine (in Mytilus edulis), derived from cysteinesulphinic acid by decarboxylation. In Arenicola cristata only the terminal reactions are different. Methionine and cysteine sulphur incorporates into taurocyamine by transamidation between taurine and arginine. 

The cysteinesulphinic acid pathway starts with the oxidation of cysteine by cysteine dioxygenase (EC 1.13.11.20). In the rat, cysteine dioxygenase is found only in the fiver and consists of two sub-units containing Cu and Fe, one catalytic and the other... 

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