title: Plasmid-mediated uptake and metabolism of sucrose by Escherichia coli K-12.
abstract: The conjugative plasmid pUR400 determines tetracycline resistance and enables cells of Escherichia coli K-12 to utilize sucrose as the sole carbon source. Three types of mutants affecting sucrose metabolism were derived from pUR400. One type lacked a specific transport system (srcA); another lacked sucrose-6-phosphate hydrolase (scrB); and the third, a regulatory mutant, expressed both of these functions constitutively (scrR). In a strain harboring pUR400, both transport and sucrose-6-phosphate hydrolase were inducible by fructose, sucrose, and raffinose; if a scrB mutant was used, fructose was the only inducer. These data suggested that fructose or a derivative acted as an endogenous inducer. Sucrose transport and sucrose-6-phosphate hydrolase were subject to catabolite repression; these two functions were not expressed in an E. coli host (of pUR400) deficient in the adenosine 3-,5'-phosphate receptor protein. Sucrose uptake (apparent Km = 10 microM) was dependent on the scrA gene product and on the phosphoenolpyruvate-dependent sugar:phosphotransferase system (PTS) of the host. The product of sucrose uptake (via group translocation) was identified as sucrose-6-phosphate, phosphorylated at C6 of the glucose moiety. Intracellular sucrose-6-phosphate hydrolase catalyzed the hydrolysis of sucrose-6-phosphate (Km = 0.17 mM), sucrose (Km = 60 mM), and raffinose (Km = 150 mM). The active enzyme was shown to be a dimer of Mr 110,000.
mesh_terms: D002876:Chromosomes, Bacterial / Q000502:physiology; D003433:Crosses, Genetic; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D005796:Genes; D005798:Genes, Bacterial; D006026:Glycoside Hydrolases / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D010957:Plasmids; D013045:Species Specificity; D013311:Streptozocin / Q000494:pharmacology; D013379:Substrate Specificity; D013395:Sucrose / Q000378:metabolism*; D043324:beta-Fructofuranosidase
chemical_list: D013395:Sucrose; D013311:Streptozocin; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase