Isolation and Some Molecular Properties of Plastidic Algal Cytochrome b-559

Cytochrome b-559, an integral protein of diloroplast thylakoids, was prepared in a homogeneous form from the alga Bum illeriopsis filiform is. The protein is easily denatured and can be solubilized by treatment of isolated thylakoids with high concentrations of urea and detergents in addition to weak sonification. The reduced form exhibits absorption maxima at 559, 530 and 429 nm. By comparative determination, a molecular weight of 17 000 was found for the protein from Bum illeriopsis, whereas that for spinach has 37 000 daltons. Both proteins have a low, but variable lipid content which is not a necessary part of the enzymatically active cytochrome b-559. The purified cytochrome exhibits a low midpoint the preparation a transient “high-potential” form