| Abstract: | The nucleic acid-independent biosynthesis of the peptide antibiotic gramicidin S results from the interaction of an enzyme bearing phenylalanine in activated form with a polyenzyme system charged with the other four component amino acids.After reaction with ATP, magnesium, and any or all of its amino acid substrates, the polyenzyme system (mol wt 280,000) yields complexes containing AMP and the respective amino acids in the proportion of 1 to 2. Similar complexes are formed by another enzyme (mol wt 100,000) on incubation with ATP, magnesium, and L- or D-phenylalanine. The amino acids are probably bound as aminoacyl adenylates and then transferred to another function on the enzyme. Initiation of polymerization is achieved by combination of the two complexes. No ATP is needed for completion of synthesis, and free intermediates are not released. Enzyme organization and specificity are responsible for the ordering of the amino acid sequence. |
