Activation of fusarium naphthazarin toxins and other p-quinones by reduced thioctic acid

Dihydrofusarubin, marticin and isomarticin are naphthazarin toxins produced by Fusarium solani, a pathogen of citrus, peas and tomato. Like other p-quinones such as 1,4-naphthoquinone, menadione or juglone, these compounds can be reductively activated by dithiols such as dihydrolipoic acid (reduced thioctic acid) or dithiothreitol but not by monothiols such as cystein or glutathione. Upon autoxidation, reduced p-quinones with appropriately negative redox potentials between -100 and -250 mV activate oxygen in a dithiol-dependent reaction producing superoxide, hydrogen peroxide and a strong oxidant similar to the OH-radical-type oxidant (<<crypto-OH>>), but apparently not identical to the free OH-radical.