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.