The Respiratory Chain of Plant Mitochondria: XVII. Flavoprotein-Cytochrome b562 Interaction in Antimycin-treated Skunk Cabbage Mitochondria 1

AUTOR(ES)

Storey, Bayard T.

RESUMO

During the transition from the aerobic steady state with succinate as substrate to anaerobiosis, in suspensions of skunk cabbage (Symplocarpus foetidus) mitochondria treated with antimycin A, cytochrome b562 becomes reoxidized to the extent of about 20%, synchronously with the reduction of cytochrome c549. This reoxidation occurs in both the absence and presence of m-chlorobenzhydroxamic acid, a specific inhibitor for the alternate terminal oxidase of plant mitochondria. A flavoprotein component, amounting to 13% to 15% of the total nonfluorescent mitochondrial flavoprotein, undergoes reduction synchronously with the oxidation of cytochrome b562 during the aerobic to anaerobic transition with succinate as substrate in the presence of both antimycin A and m-chlorobenzhydroxamic acid. This flavoprotein component remains reduced in the presence of cyanide. The half-time for reduction of the flavoprotein component and cytochrome c549 and for oxidation of cytochrome b562 during the aerobic to anaerobic transition with succinate as substrate in the presence of both antimycin A and m-chlorobenzhydroxamic acid is 2 seconds. The half-times for oxidation of cytochrome c549 and the flavoprotein component are 2.1 and 170 milliseconds, respectively, during the anaerobic to aerobic transition induced by addition of 14 μm O2 to the mitochondrial suspensions. The half-time for reduction of cytochrome b562 under these conditions is 150 milliseconds, synchronous with the flavoprotein component. The synchrony of the flavoprotein oxidation and of the cytochrome b562 reduction at a rate much slower than that of cytochrome c549 oxidation implies that, in antimycin-treated plant mitochondria, the state of the cytochrome b562/antimycin complex is regulated by the redox state of this flavoprotein component, rather than by cytochrome c549. It is tentatively suggested that these two components are not part of the main sequence of the respiratory chain, but may be part of a multienzyme complex active in the hydroxylation reactions required for ubiquinone biosynthesis in the inner mitochondrial membrane.

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