Metabolism of L-fucose and L-rhamnose in Escherichia coli: aerobic-anaerobic regulation of L-lactaldehyde dissimilation.
L-Lactaldehyde is a branching point in the metabolic pathway of L-fucose and L-rhamnose utilization. Under aerobic conditions, L-lactaldehyde is oxidized to L-lactate by the enzyme lactaldehyde dehydrogenase, while under anaerobic conditions, L-lactaldehyde is reduced to L-1,2-propanediol by the enzyme propanediol oxidoreductase. Aerobic growth on either of the methyl pentoses induces a lactaldehyde dehydrogenase enzyme which is inhibited by NADH and is very stable under anaerobic conditions. In the absence of oxygen, the cell shifts from the oxidation of L-lactaldehyde to its reduction, owing to both the induction of propanediol oxidoreductase activity and the decrease in the NAD/NADH ratio. The oxidation of L-lactaldehyde to L-lactate is again restored upon a change to aerobic conditions. In this case, only the NAD/NADH ratio may be invoked as a regulatory mechanism, since both enzymes remain active after this change. Experimental evidence in the presence of rhamnose with mutants unable to produce L-lactaldehyde and mutants capable of producing but not further metabolizing it points toward L-lactaldehyde as the effector molecule in the induction of lactaldehyde dehydrogenase. Analysis of a temperature-sensitive mutation affecting the synthesis of lactaldehyde dehydrogenase permitted us to locate an apparently single regulator gene linked to the ald locus at 31 min and probably acting as a positive control element on the expression of the structural gene.
Baldomà
L
L
Department of Biochemistry, Faculty of Pharmacy, University of Barcelona (Pedralbes), Spain.
Aguilar
J
J
D000332:Aerobiosis; D000429:Alcohol Oxidoreductases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D000447:Aldehydes / Q000378:metabolism*; D000693:Anaerobiosis; D055598:Chemical Phenomena; D002621:Chemistry; D002874:Chromosome Mapping; D004790:Enzyme Induction; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D005643:Fucose / Q000378:metabolism*; D005798:Genes, Bacterial; D005809:Genes, Regulator; D009243:NAD / Q000378:metabolism / Q000494:pharmacology; D010084:Oxidation-Reduction; D012210:Rhamnose / Q000378:metabolism*
D000447:Aldehydes; D009243:NAD; D005643:Fucose; C014634:lactaldehyde; D000429:Alcohol Oxidoreductases; C031416:D-lactaldehyde dehydrogenase; D012210:Rhamnose