title: Regulation of L-cystine transport in Salmonella typhimurium.
abstract: A kinetic analysis of L-cystine uptake in wild-type Salmonella typhimurium indicates the presence of at least two, and possibly three, separate transport systems. CTS-1 accounts for the majority of uptake at 20 muM L-cystine, with a Vmax of 9.5 nmol/min per mg and a Km of 2.0 muM; CTS-2 is a low-capacity, higher-affinity system with a Vmax of 0.22 nmol/min per mg and a Km of 0.05 muM; a third, nonsaturable process has been designated CTS-3. We find that wild-type CTS-1 levels are at least 11 times higher in sulfur-limited cells than in L-cystine-grown cells. Pleiotropic cysteine auxotrophs of the types cysE (lacking serine transacetylase) and cysB- (lacking a regulatory element of positive control) have very low levels of CTS-1 even when grown under conditions of sulfur limitation, which response is analogous to that previously observed for cysteine biosynthetic enzymes (N . M. Kredich, J. Biol. Chem. 246:3474-3484, 1971). CTS-1 is induced in cysE mutants by growth in the presence of O-acetyl-L-serine (the product of serine transacetylase), again paralleling the behavior of the cysteine biosynthetic pathway. Strain DW25, a prototrophic cysBc mutant, which is constitutive for cysteine biosynthesis, is also derepressed for CTS-1 when grown on L-cystine. Since CTS-1 is regulated by sulfur limitation, O-acetyl-L-serine, and the cysB gene product, the same three conditions controlling cysteine biosynthesis, we propose that this transport system is a part of the cysteine regulon.
mesh_terms: D001386:Azides / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D003542:Cystathionine gamma-Lyase / Q000096:biosynthesis; D003553:Cystine / Q000031:analogs & derivatives / Q000378:metabolism*; D004140:Dinitrophenols / Q000494:pharmacology; D004790:Enzyme Induction; D005809:Genes, Regulator; D007700:Kinetics; D008757:Methylglucosides / Q000494:pharmacology; D009154:Mutation; D009997:Osmotic Pressure; D012486:Salmonella typhimurium / Q000378:metabolism*; D012694:Serine / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D001386:Azides; D004140:Dinitrophenols; D008757:Methylglucosides; D012694:Serine; D003553:Cystine; D003542:Cystathionine gamma-Lyase