Fate of labeled hydroxamates during iron transport from hydroxamate-ion chelates.
The fate of the hydroxamic acid-iron transport cofactors during iron uptake from the (59)Fe(3+) chelates of the (3)H-labeled hydroxamates schizokinen and aerobactin was studied by assay of simultaneous incorporation of both (59)Fe(3+) and (3)H. In the schizokinen-producing organism Bacillus megaterium ATCC 19213 transport of (59)Fe(3+) from the (3)H-schizokinen-(59)Fe(3+) chelate at 37 C was accompanied by rapid uptake and release (within 2 min) of (3)H-schizokinen, although (3)H-schizokinen discharge was temperature-dependent and did not occur at 0 C. In the schizokinen-requiring strain B. megaterium SK11 similar release of (3)H-schizokinen occurred only at elevated concentrations of the double-labeled chelate; at lower chelate concentrations, (3)H-schizokinen remained cell-associated. Temperature-dependent uptake of deferri (iron-free) (3)H-schizokinen to levels equivalent to those incorporated from the chelate form was noted in strain SK11, but strain ATCC 19213 showed only temperature-independent binding of low concentrations of deferri (3)H-schizokinen. These results indicate an initial temperature-independent binding of the ferric hydroxamate which is followed rapidly by temperature-dependent transport of the chelate into the cell and an enzyme catalyzed separation of iron from the chelate. The resulting deferri hydroxamate is discharged from the cell only when a characteristic intracellular concentration of the hydroxamate is exceeded, which happens in the schizokinen-requiring strain only at elevated concentrations of the chelate. This strain also appears to draw the deferri hydroxamate into the cell by a temperature-dependent mechanism. The aerobactin-producing organism Aerobacter aerogenes 62-1 also demonstrated rapid initial uptake and temperature-dependent discharge of (3)H-aerobactin during iron transport from (3)H-aerobactin-(59)Fe(3+), suggesting a similar ferric hydroxamate transport system in this organism.
D001410:Bacillus megaterium / Q000254:growth & development / Q000378:metabolism*; D001693:Biological Transport, Active; D002854:Chromatography, Paper; D004579:Electron Transport; D004754:Enterobacter / Q000378:metabolism; D006877:Hydroxamic Acids / Q000096:biosynthesis / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D007502:Iron Chelating Agents / Q000096:biosynthesis / Q000378:metabolism*; D007503:Iron Isotopes; D009154:Mutation; D013696:Temperature; D014316:Tritium
D006877:Hydroxamic Acids; D007502:Iron Chelating Agents; D007503:Iron Isotopes; D014316:Tritium; D007501:Iron