Analysis of an avtA::Mu d1(Ap lac) mutant: metabolic role of transaminase C.
Escherichia coli can synthesize alpha-ketoisovalerate, the precursor of valine, leucine, and pantothenate, by three routes: anabolically via dihydroxyacid dehydrase and catabolically via both the branched-chain amino acid transaminase (transaminase B) and the alanine-valine transaminase (transaminase C). An E. coli K-12 mutant devoid of transaminase C (avtA) was isolated by mutagenizing an isoleucine-requiring strain devoid of transaminase B (ilvE::Tn5) with Mu d1(Ap lac) and selecting for valine-requiring derivatives which were ampicillin resistant, Lac+, able to crossfeed an ilvD mutant, and unable to grow on alpha-ketoisovalerate in place of valine. Strains defective in one, two, or all three alpha-ketoisovalerate metabolic enzymes were constructed, and their properties were analyzed. The data indicated that avtA is the structural gene for transaminase C, that transaminase C is a single enzyme species, and that the sole pathway for pantothenate biosynthesis is from alpha-ketoisovalerate. The data further showed that isoelectric inhibits the transaminase B-catalyzed deamination of valine in vivo.
D000613:Aminobutyrates / Q000378:metabolism; D002874:Chromosome Mapping; D002876:Chromosomes, Bacterial; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D005796:Genes; D045782:Hemiterpenes; D006836:Hydro-Lyases / Q000378:metabolism; D007651:Keto Acids / Q000096:biosynthesis; D009154:Mutation; D010205:Pantothenic Acid / Q000096:biosynthesis; D000637:Transaminases / Q000235:genetics / Q000378:metabolism*
D000613:Aminobutyrates; D045782:Hemiterpenes; D007651:Keto Acids; D010205:Pantothenic Acid; C001505:alpha-ketoisovalerate; C012223:alpha-aminobutyric acid; D000637:Transaminases; C019798:branched-chain-amino-acid transaminase; C034522:valine-pyruvate transaminase; D006836:Hydro-Lyases; C020052:dihydroxyacid dehydratase