The decarboxylation of L-phenylalanine by Streptococcus faecalis R.

Gale (1) and Epps (2) have reported the properties of an enzyme obtained from various strains of Streptococcus faecalis which decarboxylates tyrosine and dihydroxyphenylalanine. Both of these authors reported that the enzyme preparations, whether made by washing the whole organism, by drying the cells with acetone, or by further purification procedures, were specific to the above two amino acids. In the course of studies in which we were employing an acetone powder of Streptococcus faecak R as a reagent for the estimation of tyrosine in the presence of other amino acids, we noticed that under certain conditions the medium apparently contained more tyrosine than the amount originally added. TJpon investigation, this proved t’o be due to a concomitant decarboxylation of phenylalanine by t,he decarboxylase preparation. The culture of the organism and the preparation of the acetone powder have been previously described (2). We employed a medium containing 30 gm. of casein acid hydrolysate (Stearns, amino acids 20 per cent solution), 10 gm. of glucose, and 5 gm. of dried yeast extract (Difco) per liter, sufficient dipotassium phosphat,e being added to bring the pII up t,o 6.0. The organism was grown at 37” for 16 hours. All measurements were made with the Warburg apparatus at 38” with nitrogen as the gas phase, the acetone powder being added from the side arm as a suspension in 0.3 M citrate buffer, pH 5.4. The main compartment contained the substrates in the same buffer. The L-phenylalanine employed gave no color with the Millon’s test for tyrosine. Fig. 1 illustraks the decarboxylation of 16 micromoles of I,-phenylalanine by 50 mg. of the acet’one powder. The reaction is 98 per cent completed in 6 hours under these conditions. In similar experiments, 60 mg. of the enzyme preparation caused 100 per cent decarboxylation of the amino acid in the same time. We could demonstrate no effect of the presence of L-phenylalanine on the decarboxylation of L-tyrosine by the preparation (Fig. 2), even though 40 micromoles of L-phenylalanine were added as compared to 5 micromoles