As if running around nitroslyating things weren't bad enough, peroxynitrite unleashes hell on the electron transport chain in the mitochondria, which of course are already in trouble. Peroxynitrite nitrosylates cytochrome c  oxidase, and probably other respiratory proteins as well.

Moreover, both ^.NO itself and, probably, peroxynitrite-induced mitochondrial stress promote additional superoxide production, which reacts with ^.NO to form more peroxynitrite.