The biosynthetic pathway of 3-amino-5-hydroxybenzoic
acid (AHBA) formation was studied with cell-free extracts from the rifamycin B producer, Amycolatopsis
mediterranei S699, and the ansatrienin A producer,
Streptomyces collinus Tü1892. Phosphoenolpyruvate
(PEP) plus erythrose 4-phosphate (E4P) gave AHBA in low
but nevertheless significant (6%) yield.
3,4-Dideoxy-4-amino-d-arabino-heptulosonic
acid 7-phosphate (aminoDAHP)
was converted efficiently into AHBA (45%), as were
5-deoxy-5-amino-3-dehydroquinic acid (aminoDHQ, 41%)
and 5-deoxy-5-amino-3-dehydroshikimic acid (aminoDHS, 95%). On
the other hand, the normal shikimate pathway
intermediate, 3-deoxy-d-arabino-heptulosonic
acid 7-phosphate (DAHP) did not give rise to AHBA under
these
conditions. AminoDAHP (9%) was produced by incubation of
[14C]PEP and E4P, but not of
[14C]DAHP, with the
cell-free extracts. The results demonstrate the operation of a new
variant of the shikimate pathway in the formation
of the mC7N units of ansamycin, and presumably also
mitomycin, antibiotics which leads from PEP, E4P, and a
nitrogen source directly to aminoDAHP and then via aminoDHQ and
aminoDHS to AHBA.
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