The biosynthesis of the antibiotic pyrrolnitrin by Pseudomonas aureofaciens

Feeding experiments with tryptophan samples labeled specifically with radioactive and stable isotopes have shown that Pseudomonas aureofaciens converts this amino acid into pyrrolnitrin in such a way that the indole nitrogen gives rise to the nitro group, the amino group becomes the pyrrole nitrogen, C-3 of the precursor side chain becomes C-3 of the antibiotic, and H-2 of the indole ring and H-alpha of the side chain give rise to H-5 and H-2 of pyrrolnitrin, respectively. Only the L-isomer of tryptophan is incorporated with retention of the alpha-hydrogen and the amino nitrogen. From the D-isomer the labels from these two positions are lost. The obvious conclusion that L-tryptophan is the more immediate precursor is, however, contradicted by the better incorporation of D- than L-tryptophan into the antibiotic. Several potential pathway intermediates were evaluated for incorporation and 4-(0-aminophenyl)-pyrrole was found to be a good precursor. The results area discussed in terms of a plausible pathway for pyrrolnitrin biosynthesis.