Alanine and Aspartate Formation During Growth on Valine-C14 by Pseudomonas aeruginosa

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Sokatch, J. R. (University of Oklahoma School of Medicine, Oklahoma City). Alanine and aspartate formation during growth on valine-C14 by Pseudomonas aeruginosa. J. Bacteriol. 92:72–75. 1966.—Pseudomonas aeruginosa grown with dl-valine-4,4′-C14 synthesized alanine labeled mainly in carbons 1 and 3, indicating that the isopropyl carbons of valine were the precursors of pyruvate for alanine formation by a pathway which did not involve randomization of isotope. Alanine from cells grown on valine-1-C14 contained isotope only in the carboxyl carbon, suggesting another route to pyruvate from valine by carbon dioxide fixation. Oxidation of valine to propionyl-coenzyme A (CoA), as it occurs in animal tissues, followed by the oxidation of propionyl-CoA to acrylyl-CoA, lactyl-CoA, and pyruvate, would account for the isotope data. Cells grown on valine oxidized valine, isobutyrate, and propionate immediately, whereas cells grown on acetate did not oxidize valine or isobutyrate and required an induction period before propionate was oxidized. P. aeruginosa grown with propionate-1-C14 or propionate-2-C14 formed alanine-1-C14 and alanine-2-C14, respectively, which agrees with the contention that at least part of the propionate is oxidized via the acrylate pathway. Aspartate formed from valine-1-C14 was labeled only in the carboxyl carbons, whereas that formed from valine-4,4′-C14 was labeled in all four carbons, but most heavily in carbons 1 and 3. These data suggest that the main route for the formation of the carbon skeleton of aspartate was by a C3 plus C1 condensation, with the C3 unit derived from the isopropyl carbons of valine and the C1 unit probably from carbon dioxide.

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