Biosynthesis of gramicidin S II. Incorporation experiments with labeled amino acid analogs, and the amino acid activation process

Abstract

Experiments in which labeled amino acid analogs were added to growing cultures of B. brevis suggest that a fairly high degree of substrate specificity exists in the process of gramicidin formation. d-Phenylalanine could be replaced to a limited extent by dl-thienylalanine, while radioactive dl-p-fluorophenylalanine and dl-norleucine gave rise to low concentrations of isotope in the polypeptide. Certain analogs of valine, ornithine, and proline were not incorporated into gramicidin. The results of studies with cell extracts are in accord with the view that amino acid activation, as reflected in pyrophosphate-adenosine triphosphate exchange, may be a primary stage in gramicidin biosynthesis.