Characterization of the lactose transport system in Citrobacter freundii.
The lactose transport system of Citrobacter freundii was characterized. Both the lactose transport system and beta-galactosidase were induced with either lactose or isopropyl-beta-D-thiogalactopyranoside (IPTG), the latter being the better inducer. The Km values for methyl-beta-D-thiogalactopyranoside (TMG) transport and lactose transport were 0.61 mM and 1.1 mM, respectively, and the Vmax values were 53 nmol/min/mg cell protein and 12 nmol/min/mg cell protein, respectively. Thus, TMG is a better substrate than lactose. Thiogalactopyranoside (TDG) was a very potent competitive inhibitor. Neither Na+ nor Li+ had a significant effect on the TMG transport or the lactose transport. Proton/substrate cotransport (symport) via this system was observed.
Department of Microbiology, Faculty of Pharmaceutical Sciences, Okayama University, Japan.
N
N
Okazaki
M
M
Tsuda
T H
TH
Wilson
T
T
Tsuchiya
D016971:Citrobacter freundii / Q000201:enzymology*; D004790:Enzyme Induction / Q000187:drug effects; D007544:Isopropyl Thiogalactoside / Q000494:pharmacology; D007785:Lactose / Q000378:metabolism*; D008756:Methylgalactosides / Q000494:pharmacology; D013379:Substrate Specificity; D013862:Thiogalactosides / Q000494:pharmacology; D001616:beta-Galactosidase / Q000378:metabolism*
D008756:Methylgalactosides; D013862:Thiogalactosides; C009468:thiomethylgalactoside; D007544:Isopropyl Thiogalactoside; D001616:beta-Galactosidase; D007785:Lactose