Abstract
Summary
Two different strains of the bacterium, Bacillus brevis, each of which produces the antibiotic, cyclic, decapeptides called tyrocidines have been studied. The four tyrocidines differ only in the position occupied by three of their four aromatic amino acid residues. Two of these positions may be occupied by either phenylalanine or tryptophan and the third by tyrosine or tryptophan, with the substitutions occurring in a definite sequence. (See structures given in the introductory paragraphs). A report that these four peptides are produced in vivo, by a single enzyme system with a low specificity for the aromatic amino acids, was confirmed with cell-free extracts in which the possibility of protein synthesis could be excluded. A second strain of the bacterium yielded extracts which did not show how this lack of specificity.
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