Quinone interaction with the respiratory chain-linked NADH dehydrogenase of beef heart mitochondria I. Juglone reductase activity

Abstract

1. Substituted benzoquinones and napthoquinones can function as electron acceptors for the NADH dehydrogenase segment of the mitochondrial electron transport system. Anthraquinones and several hydroxylated quinones are not reduced by the enzyme complex. 2. Piericidin A treatment at concentrations known to inhibit electron transport causes varying degrees of inhibition of quinone reductase activities. The pattern of piericidin A inhibition suggests that certain quinones are reduced at sites either before or after the piericidin A inhibition site. Reduction of quinones such as 5-hydroxy-1,4-napthoquinone (juglone) and 1,2-napthoquinone is inhibited only slightly. Reduction of ubiquinone 1 and 2 and 2,3,5,6-tetramethyl-1,4-benzoquinone (duroquinone) is almost completely inhibited following piericidin A treatment. 3. Comparison of juglone reductase activity with ferricyanide reductase activity suggests that these acceptors are reduced at nonequivalent sites in the NADH dehydrogenase. Juglone reductase activity is stimulated following mercurial treatment while ferricyanide reductase activity is slightly inhibited. Preincubation of NADH dehydrogenase with NADH followed by mercurial treatment causes almost complete inhibition of ferricyanide reductase activity. Activation of juglone reductase activity still occurs under these conditions. The activation is specific for preparations of NADH dehydrogenase, for mercurials, and for napthoquinone reductase activity.