In the course of our screening for new antibiotic, newmembersof benz[a]anthraquinone antibiotics (I and II), which showed antibacterial activity against Gram-positive bacteria were isolated from a culture broth of Streptomyces tsusimaensis MI310-38F7. This strain produced nonactin and a minor yellow compound (III) which was identical with X-14881 E1}. This report describes the isolation, characterization and structure determination of these compounds, named 6-deoxy-8-0-methylrabelomycin (I) and 8-0-methylrabelomycin (II).
Probestin has been isolated as part of a program designed to find microorganism-produced inhibitors of aminopeptidase Mfrom Streptomyces azureus MH663-2F6.It was purified by use of column chromatography of Amberlite XAD-4, silica gel, YMC-gel, Toyopearl HW-40, YMC D-ODS-5(HPLC) and then isolated as colorless powders. Probestin is competitive with the substrate, and the inhibition constant (Ki) of it was 1.9 x 10"8 m.
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