The effect of four biologically active and naturally occurring plant quinones, namely maesanin, maesaquinone, embelin and juglone on the respiration of mitochondria isolated from Glossina morsitans morsitans, Schistoscerca gregaria and Periplaneta americana was investigated. The rate of oxygen consumption by the mitochondria was measured using an oxygen electrode. Maesanin inhibited the mitochondrial electron transport chain at a level before cytochrome C whereas maesaquinone and embelin uncoupled the mitochondria. Juglone inhibited respiration in G. m. morsitans mitochondria and uncoupled those of S. gregaria and P. americana.
