Protactin is a pentapeptide lactone produced by Streptomyces cucumeris strain L703-4 (ATCC 53784) with significant antioxidant properties. Protactin can be converted to actinomycin Zp by ferrocyanide oxidation. Actinomycin Zp exhibits potent antibacterial activity in vitro and has significant antitumor effects against P-388 leukemia in a mouse model.