UTILIZATION OF PHENYLALANINE, PHENYLLACTIC ACID, AND PHENYLPYRUVIC ACID BY LACTOBACILLUS CASEI

In previous reports (1, 3) the authors have shown that Lactobacillus casei (ATCC 7469) responds equally well to phenylalanine, phenyllactic acid, or phenylpyruvic acid.It was demonstrated also that P-2-thienylalanine inhibited the utilization of phenylalanine but not of phenyllactic acid.Since the latter observation was not in harmony with the view that phenyllactic acid is a precursor of phenylalanine, this problem was investigated further, with the results described in the present paper. EXPERIMENTALThe media and the assay procedure were those described previously (1, 3).Inhibitors were introduced into the basal medium as solids or as aqueous solutions.Results m-and p-Fluorophenyl-DL-alanines'-The response of L. casei to these inhibitors is given in Table I.The utilization of L-phenylalanine was inhibited completely by p-fluorophenylalanine at a weight ratio of 3: 1 of inhibitor to metabolite and by m-fluorophenylalanine at a ratio of 10: 1.The utilization of phenyl-m-lactic acid was inhibited about 10 per cent by p-fluorophenylalanine at a concentration of 100 y of inhibitor per tube over a range of 1 to 28 y of the hydroxy acid.Inhibition by m-fluorophenylalanine was negligible.The utilization of phenylpyruvic acid was inhibited only slightly by p-fluorophenylalanine and not at all by the meta compound.DL-Mandelic Acid-The response of L. casei to mandelic acid is presented