title: Natural and altered induction of the L-fucose catabolic enzymes in Klebsiella aerogenes.
abstract: Mutants of Klebsiella aerogenes W70 were isolated that had gained the ability to utilize the uncommon pentose D-arabinose as their sole source of carbon and energy. In contrast to the D-arabinose-negative, parent strain, these mutants were found to be either constitutive for certain enzymes of the L-fucose catabolic pathway or inducible for such enzymes when incubated in the presence of D-arabinose. The mutants used L-fucose isomerase to convert D-arabinose to D-ribulose, which is an intermediate and inducer of the ribitol catabolic pathway. The D-ribulokinase of the ribitol pathway was then induced. This enzyme catalyzed the phosphorylation of D-ribulose at the 5-carbon position. Mutants that were negative for D-ribulokinase could still dissimilate D-arabinose slowly by using all three enzymes, the isomerase, kinase, and aldolase, of the L-fucose pathway. Using condition negative mutants, we were able to demonstrate that the natural induction of the L-fucose pathway enzymes by L-fucose required the activity of a functional L-fucose isomerase and a functional L-fuculokinase but not an L-fuculose-1-phosphate aldolase. A metabolic intermediate, L-fuculose-1-phosphate, was thereby shown to be a probable inducer of at least the isomerase and kinase of the L-fucose catabolic pathway. Similar experiments, with D-arabinose-positive mutants, which were induced for the L-fucose pathway enzymes upon incubation with D-arabinose, revealed that the activities of the L-fucose isomerase and the L-fuculokinase were also required for the induction of the L-fucose enzymes. These D-arabinose-positive mutants apparently produced an altered regulatory protein that accepted both L-fuculose-1-phosphate and D-ribulose-1-phosphate as inducers. Examination of constitutive mutants revealed that L-fucose isomerase and L-fuculokinase were both synthesized constitutively, with the aldolase apparently under separate control.
mesh_terms: D000446:Aldehyde-Lyases / Q000096:biosynthesis* / Q000378:metabolism; D001089:Arabinose / Q000378:metabolism; D002238:Carbohydrate Epimerases / Q000096:biosynthesis* / Q000378:metabolism; D002474:Cell-Free System; D004754:Enterobacter / Q000201:enzymology* / Q000378:metabolism; D004755:Enterobacteriaceae / Q000201:enzymology*; D004790:Enzyme Induction; D005643:Fucose / Q000378:metabolism*; D009154:Mutation; D010770:Phosphotransferases / Q000096:biosynthesis* / Q000378:metabolism; D012274:Ribulosephosphates / Q000096:biosynthesis; D013237:Stereoisomerism; D013696:Temperature
chemical_list: D012274:Ribulosephosphates; D005643:Fucose; D001089:Arabinose; D010770:Phosphotransferases; D000446:Aldehyde-Lyases; D002238:Carbohydrate Epimerases