Investigations of amino acids, peptides, and proteins; the determination of phenylalanine in protein hydrolysates with Leuconostoc mesenteroides P-60 and Lactobacillus casei.

During the past 2 years microbiological procedures’ have been reported for the determination in proteins of thirteen of the twenty-one amino acids which occur in protein materials. Seven amino acids (isoleucine, glutamic acid, methionine, leucine, phenylalanine, tryptophane, and valine) have been determined with Lactobacillus arabinosus 17-5, three (arginine, tyrosine, and valine) with Lactobacillus casei, two (histidine and lysine) with Leuconostoc mesenteroides P-60, two (aspartic acid and serine) with Lactobacillus delbriickii (4), and one (tryptophane) with Eberthella typhosa T-63 (5). Comparable methods (unpublished) have been developed in the authors’ laboratory for the determination of cystine, glycine, and threonine. It is possible, therefore, to determine microbiologically all of the accepted amino acids except alanine, proline, hydroxyproline, 3,5diiodotyrosine, and thyroxine. It has been shown, previously, that phenylalanine2 is essential for the growth of Clostridium sporogenes (7), Corynebacterium diphtheriae (8), Streptococcus hemolyticus (9)) Lactobacillus mannitopoeus (lo), Lactobacillus buchneri (lo), Lactobacillus lycopersici (lo), Lactobacillus delbriickii (II), Lactobacillus arabinosus 17-5 (12-16), Lactobacillus casei (3,17), and Leuconostoc mesenteroides P-60 (18). Although Hegsted (15) has assayed phenylalanine with Lactobacillus arabinosus 17-5, the present studies were undertaken