Diaphorase-mediated oxygen activation and uncoupling of mitochondrial electron transport by naphthazarin toxins produced by Fusarium solani

Naphthazarin toxins such as dihydrofusarubin, marticin, isomarticin and methyljavanicin are produced by Fusarium solani, a pathogen for citrus, peas and tomatoes. Similar to other p-quinones such as several members of the anthraquinone- or 1,4-naphthoquinone-families, dihydrofusarubin, marticin, and isomarticin were reductively activated by diaphorases at the expense of NAD(P)H. Upon autoxidation, the reduced compounds activated oxygen, forming superoxide and hydrogen peroxide. Finally, a strong oxidant similar to the OH-radical was produced in an iron-dependent reaction. The Fusarium solani toxins did not show redox-coupling with isolated mitochondria neither at the expense of NADH nor of succinate. However, the naphthazarin derivates marticin, isomarticin and methyljavanicin, but not dihydrofusarubin, acted as uncouplers of the mitochondrial electron transport chain.