title: Uptake and metabolism of sucrose by Streptococcus lactis.
abstract: Transport and metabolism of sucrose in Streptococcus lactis K1 have been examined. Starved cells of S. lactis K1 grown previously on sucrose accumulated [14C]sucrose by a phosphoenolpyruvate-dependent phosphotransferase system (PTS) (sucrose-PTS; Km, 22 microM; Vmax, 191 mumol transported min-1 g of dry weight of cells-1). The product of group translocation was sucrose 6-phosphate (6-O-phosphoryl-D-glucopyranosyl-1-alpha-beta-2-D-fructofuranoside). A specific sucrose 6-phosphate hydrolase was identified which cleaved the disaccharide phosphate (Km, 0.10 mM) to glucose 6-phosphate and fructose. The enzyme did not cleave sucrose 6'-phosphate(D-glucopyranosyl-1-alpha-beta-2-D-fructofuranoside-6'-phosphate). Extracts prepared from sucrose-grown cells also contained an ATP-dependent mannofructokinase which catalyzed the conversion of fructose to fructose 6-phosphate (Km, 0.33 mM). The sucrose-PTS and sucrose 6-phosphate hydrolase activities were coordinately induced during growth on sucrose. Mannofructokinase appeared to be regulated independently of the sucrose-PTS and sucrose 6-phosphate hydrolase, since expression also occurred when S. lactis K1 was grown on non-PTS sugars. Expression of the mannofructokinase may be negatively regulated by a component (or a derivative) of the PTS.
mesh_terms: D001692:Biological Transport; D004790:Enzyme Induction; D005631:Fructokinases / Q000302:isolation & purification / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D013294:Lactococcus lactis / Q000378:metabolism*; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism*; D013395:Sucrose / Q000378:metabolism*; D043324:beta-Fructofuranosidase
chemical_list: D013395:Sucrose; D010770:Phosphotransferases; D005631:Fructokinases; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C027295:mannofructokinase; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase