Lipoic Acid Synthesis Research Articles

Possible involvement of lipoic acid in binding protein-dependent transport systems in Escherichia coli.

We describe the properties of the binding protein dependent-transport of ribose, galactose, and maltose and of the lactose permease, and the phosphoenolpyruvate-glucose phosphotransferase transport systems in a strain of Escherichia coli which is deficient in the synthesis of lipoic acid, a cofactor involved in alpha-keto acid dehydrogenation. Such a strain can grow in the absence of lipoic acid in minimal medium supplemented with acetate and succinate. Although the lactose permease and the phosphoenolypyruvate-glucose phosphotransferase are not affected by lipoic acid deprivation, the binding protein-dependent transports are reduced by 70% in conditions of lipoic acid deprivation when compared with their activity in conditions of lipoic acid supply. The remaining transport is not affected by arsenate but is inhibited by the uncoupler carbonylcyanide-m-chlorophenylhydrazone; however the lipoic acid-dependent transport is completely inhibited by arsenate and only weakly inhibited by carbonylcyanide-m-chlorophenylhydrazone. The known inhibitor of alpha-keto acid dehydrogenases, 5-methoxyindole-2-carboxylic acid, completely inhibits all binding protein-dependent transports whether in conditions of lipoic supply or deprivation; the results suggest a possible relation between binding protein-dependent transport and alpha-keto acid dehydrogenases and shed light on the inhibition of these transports by arsenicals and uncouplers.

Synthesis of lipoic acid by Streptococcus faecalis 10C1 and end-products produced anaerobically from low concentrations of glucose.

SUMMARY Streptococcus faecalis IOCI and 6783 grew anaerobically on glucose in media lacking lipoic acid and acetate, and assays with Streptococcus cremoris KH indicated that extracts of S. faecalis IOCI contained lipoic acid activity equivalent to 200 ng of a-D,L-lipoic acid/mg protein. The Yslllcose value for a continuous culture of strain IOCI grown anaerobically in lipoic acid-deficient medium was 37.2, about the same as that for IOCI in lipoic acid-sufficient medium (35.5). Strains IOCI and 6783 metabolized low concentrations of glucose (I to 8 pmol/ml) non-homolactically and produced per mol of glucose about 1.0 mol lactate, 1-2 mol acetate, and 0.4 mol ethanol. Appreciable amounts of pyruvate, formate, glycerol, acetoin, diacetyl, and 2,3-butylene glycol were not detected. The Yglucoee values for strain IOCI were lower (25, 17 and 21, respectively) if IO-~ M-arsenite or 0.5 % acetate was added or the pH value in the fermentor was decreased to 5.3. With acetate added or the pH value reduced, the glucose was metabolized mostly to lactate. Results indicate that S. Jizecalis IOCI used the pyruvate-dehydrogenase-enzyme complex rather than the phosphoroclastic mechanism in metabolizing anaerobically to acetate approximately half of the pyruvate produced from low concentrations of glucose.