Protactin, a new antibiotic metabolite and a possible precursor of the actinomycins.

Streptomyces cucumerosporus strain L703-4 (ATCC 53784) produces a new 4-methyl-3-hydroxyanthraniloylpentapeptide lactone for which we have proposed the name protactin, in addition to several actinomycin components. Protactin is rather resistant to air oxidation but it can be converted to a new actinomycin, actinomycin Zp by ferricyanide oxidation. Actinomycin Zp possesses in vitro antibacterial activity and in vivo antitumor activity against P-388 leukemia in mice.