title: An evaluation of the in vivo metabolism of cystine in Escherichia coli using stable isotopes.
abstract: The incorporation of deuterated serine into cysteine during the metabolism of cystine by Escherichia coli was studied in order to determine the extent to which the carbon-sulfur bond(s) of the cystine is cleaved. The results indicate that the major route (approximately 80%) for cystine metabolism consists of a reductive cleavage of the cystine disulfide bond to form cysteine. Evidence is presented which shows that a portion of the remaining cystine is broken down by a pathway(s) which results in cleavage of the carbon-sulfur bond of the cystine. This pathway would be the same as that expected for the beta-elimination of pyruvate from cystine catalysed by the enzyme beta-cystathionase. In addition, a small portion of the resulting cysteine is shown to undergo a reversible dissociation to serine and hydrogen sulfide. Evidence is presented which shows that this dissociation is caused by the enzyme cysteine synthetase [O-acetyl-L-serine acetate-lyase (adding H2S)].
mesh_terms: D003470:Culture Media; D003553:Cystine / Q000378:metabolism*; D003903:Deuterium; D004926:Escherichia coli / Q000378:metabolism*; D008715:Methionine / Q000378:metabolism; D012694:Serine / Q000378:metabolism
chemical_list: D003470:Culture Media; D012694:Serine; D003553:Cystine; D008715:Methionine; D003903:Deuterium