title: L-asparagine uptake in Escherichia coli.
abstract: The uptake of L-asparagine by Escherichia coli K-12 is characterized by two kinetic components with apparent Km values of 3.5 muM and 80 muM. The 3.5 muM Km system displays a maximum velocity of 1.1 nmol/min per mg of protein, which is a low value when compared with derepressed levels of other amino acid transport systems but is relatively specific for L-asparagine. Compounds providing effective competition for L-asparagine uptake were 4-carbon analogues of the L-isomer with alterations at the beta-amide position, i.e., 5-diazo-4-oxo-L-norvaline (Ki = 4.6 muM), beta-hydroxyamyl-L-aspartic acid (Ki = 10 muM), and L-aspartic acid (Ki = 50 muM). Asparagine uptake is energy dependent and is inhibited by a number of metabolic inhibitors. In a derived strain of E. coli deficient in cytoplasmic asparaginase activity asparagine can be accumulated several-fold above the apparent biosynthetic pool of the amino acid and 100-fold above the external medium. The high affinity system is repressed by culture of cells with L-asparagine supplements in excess of 1 mM and is suggested to be necessary for growth of E. coli asparagine auxotrophs with lower supplement concentrations.
mesh_terms: D001216:Asparagine / Q000031:analogs & derivatives / Q000378:metabolism*; D001667:Binding, Competitive; D001693:Biological Transport, Active / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007773:Lactates / Q000378:metabolism; D008314:Malonates / Q000494:pharmacology; D010070:Oxalates / Q000494:pharmacology; D010072:Oxamic Acid / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013386:Succinates / Q000378:metabolism; D013696:Temperature
chemical_list: D007773:Lactates; D008314:Malonates; D010070:Oxalates; D013386:Succinates; D001216:Asparagine; D012964:Sodium; D005947:Glucose; D010072:Oxamic Acid