Effect of ATP on the redox cycle of respiratory chain-linked DPNH dehydrogenase and the localization of coupling site I

Abstract

On adding DPNH to a phosphorylating membrane preparation in the presence of O 2 the reduction of a chromophore, which has been tentatively identified as nonheme iron of DPNH dehydrogenase, may be observed by dual wavelength spectrophotometry at 470–500 mμ. With rotenone or piericidin present a part of the chromophore remains permanently bleached even after exhaustion of the DPNH. ATP, however, causes rapid and complete reoxidation of the chromophore. This effect is abolished by oligomycin and dinitrophenol. Control experiments show that under these conditions the rotenone block between DPNH dehydrogenase and cytochrome b is substantially complete. Analysis of the data suggest that coupling site I is located between the specific binding site of rotenone and the nonheme irons responsible for the g=1.94 signal, both of which appear to be constituents of DPNH dehydrogenase.