Phenylalanine stimulation of gramicidin S formation

Bacillus brevis produces the antibiotic gramicidin S, a cyclic peptide comprised of two pentapeptide units of the sequence d-Phe-l-Pro-l-Val-l-Orn-l-Leu. Synthesis of this antibiotic is carried out by two enzymes, GS synthetases I and II. By supplementing a defined minimal medium [glycerol, NH(4) (+), tris(hydroxymethyl)aminomethane, salts] with each of the constituent amino acids (in the l form), we found that only l-phenylalanine had a marked stimulatory effect on gramicidin S production. This effect was not caused by an increase in growth, by an induction of GS synthetases I or II, or by a stabilization of these enzymes. l-Phenylalanine apparently stimulates production via its role as a precursor of the d-phenylalanine moiety of the gramicidin S molecule.