Partial purification and characterization of a blue light-sensitive cytochrome-flavin complex from corn membranes

A membrane fraction which contains a blue light-sensitive flavin-cytochrome complex (Brain et al. 1977 Plant Physiol 59:948) has been partially purified by sucrose and Renografin gradient centrifugations. Assays for marker enzymes show that this membrane fraction is distinct from endoplasmic reticulum, golgi, and mitochondria. This membrane fraction co-sedimented with glucan synthetase II activity, a proposed marker for plasma membrane in higher plants. The purified membrane fraction shows virtually identical light minus dark and dithionite reduced minus oxidized difference spectra with difference bands near 427 and 557 nanometers, suggesting that contamination by other cytochrome-containing membrane fractions is not significant. The photoactivity can be completely solubilized by 0.1% Triton X-100, leaving the bulk of the membrane undissolved. The kinetics for cytochrome photoreduction are not significantly affected by solubilization, indicating that both flavin and cytochrome could be associated with the same protein moiety.