Biochemical characterization of a fructokinase mutant of Rhizobium meliloti.
A double mutant strain (UR3) of Rhizobium meliloti L5-30 was isolated from a phosphoglucose isomerase mutant (UR1) on the basis of its resistance to fructose inhibition when grown on fructose-rich medium. UR3 lacked both phosphoglucose isomerase and fructokinase activity. A mutant strain (UR4) lacking only the fructokinase activity was derived from UR3; it grew on the same carbon sources as the parent strain, but not on fructose, mannitol, or sorbitol. A spontaneous revertant (UR5) of normal growth phenotype contained fructokinase activity. A fructose transport system was found in L5-30, UR4, and UR5 grown in arabinose-fructose minimal medium. No fructose uptake activity was detected when L5-30 and UR5 were grown on arabinose minimal medium, but this activity was present in strain UR4. Free fructose was concentrated intracellularly by UR4 > 200-fold above the external level. A partial transformation of fructose into mannitol and sorbitol was detected by enzymatic analysis of the uptake products. Polyol dehydrogenase activity was detected in UR4 grown in arabinose-fructose minimal medium. The induction pattern of polyol dehydrogenase activities in this strain might be due to slight intracellular fructose accumulation.
D000429:Alcohol Oxidoreductases / Q000378:metabolism; D005631:Fructokinases / Q000378:metabolism*; D005632:Fructose / Q000378:metabolism; D005956:Glucose-6-Phosphate Isomerase / Q000378:metabolism; D008353:Mannitol / Q000378:metabolism; D009154:Mutation; D010770:Phosphotransferases / Q000378:metabolism*; D012231:Rhizobium / Q000201:enzymology* / Q000235:genetics; D013012:Sorbitol / Q000378:metabolism
D005632:Fructose; D008353:Mannitol; D013012:Sorbitol; D000429:Alcohol Oxidoreductases; D010770:Phosphotransferases; D005631:Fructokinases; D005956:Glucose-6-Phosphate Isomerase