Studies of etamycin biosynthesis employing short-term experiments with radiolabeled precursors.

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Abstract
The biosynthesis of etamycin by Streptomyces griseoviridus was investigated with the precursors, 14C-L-leucine and 14CH3-L-methionine, during short-term incubations. Both radioisotopes are rapidly incorporated into the antibiotic without significant lag. D-Leucine, but not L-leucine, inhibits etamycin formation. The kinetics of incorporation of 14C-L-leucine as well as the inhibitor studies suggest that L-leucine is the direct precursor of the D-enantiomer present in the antibiotic peptide. Chloramphenicol inhibits protein synthesis by S. griseoviridus without reduction of etamycin formation, indicating that a non-ribosomal mechanism of synthesis is involved in etamycin biogenesis. When L-ethionine was employed, both formation of antibiotic and protein were blocked.