A BLUE LIGHT-SENSITIVE CYTOCHROME-FLAVIN COMPLEX FROM CORN COLEOPTILES. FURTHER CHARACTERIZATION

Abstract

— The partially purified blue light-sensitive membrane-associated flavin-cytochrome complex from etiolated corn coleoptiles shows a unique sharp α-band at 555 nm in its light-minus-dark difference spectrum at liquid nitrogen temperature. This band is clearly distinguishable from the α-bands found in fractions enriched for mitochondria and endoplasmic reticulum respectively. The photoactive membrane fraction is shown to have ATPase activity that is not stimulated by K+ and that is not inhibited by oligomycin. Other than flavin fluorescence at 525 nm obtained upon excitation at 450 nm, there is a second fluorescent component with emission at 430 nm on excitation at 350 nm. The mid-point potential of the Triton X-100 solubilized b-cytochrome, measured by simultaneously monitoring the reduction of the pyocyanine 600-800 nm peak and the appearance of the 427 nm Soret peak of the b-cytochrome upon titration with dithionite in the presence of ferricyanide, is estimated to be −65 mV. The kinetics of the blue light-induced reduction and dark rcoxidation of the 6-cytochrome suggest that the mid-point potential of the b-cytochrome is not affected by Triton X-100 solubilization.