Green algal cytochrome b₆-f complexes: isolation and characterization from Dunaliella saline, Chlamydomonas reinhardtii and Scenedesmus obliquus

Cytochrome b₆-f complexes have been isolated from Chlamydomonas reinhardtii, Dunaliella saline and Scenedesmus obliquus. Each complex is essentially free of chlorophyll and carotenoids and contains cytochrome b₆ and cytochrome f hemes in a 2:1 molar ratio. C. reinhardtii and S. obliquus complexes contain the Rieske iron-sulfur protein (present in approx 1:1 molar ratio to cytochrome f) and each catalyzes a DBMIB- and DNP-INT-sensitive electron transfer from duroquinol to spinach plastocyanin. Immunological assays using antibodies to the peptides from the spinach cytochrome complex show varying cross-reactivity patterns except for the complete absence of binding to the Rieske protein in any of the three complexes, suggesting little structural similarity between the Rieske proteins of algae with those from higher plants. One complex (D. salina) has been uniformly labeled by growth in NaH¹⁴CO₃ to determine stoichiometries of constituent polypeptide subunits. Results from these studies indicate that all functionally active cytochrome b₆-f complexes contain four subunits which occur in equimolar amounts.