The Aurachins, Naturally Occurring Inhibitors of Photosynthetic Electron Flow through Photosystem II and the Cytochrome b j f -Complex

A third group o f antibiotics, the aurachins, have been isolated from the m yxobacterium Stigmatella aurantiaca. The aurachins chemically are quinolones, and four o f them (aurachins A D ) have been tested for their inhibitory activity in photosystem II and cytochrom e b/ccomplexes. A urachin C is the best inhibitor in photosystem II (p /50-value 7.2); its biochemical behaviour being the same like tha t o f other photosystem II herbicides. Both aurachins C and D are also excellent inhibitors in the cytochrom e b{ respectively). In its m echanism o f action, aurachin C is different from either antim ycin or myxothiazol.