Characterization of the cytochrome b6f complex from marine green alga, Bryopsis corticulans

A pure, active cytochrome b₆f was isolated from the chloroplasts of the marine green alga, Bryopsiscorticulans. To investigate and characterize this cytochrome b₆f complex, sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE), absorption spectra measurement and HPLC were employed. It was shown that this purified complex contained four large subunits with apparent molecular masses of 34.8, 24, 18.7 and 16.7 kD. The ratio of Cyt b₆ to Cytf was 2.01 : 1. The cytochromeb₆f was shown to catalyze the transfer of 73 electrons from decylplastoquinol to plastocyanin–ferricyanide per Cyt f per second. α-Carotene, one kind of carotenoid that has not been found to present in cytochrome b₆f complex, was discovered in this preparation by reversed phase HPLC. It was different from β-carotene usually found in cytochrome b₆f complex. The configuration of the major α-carotene component was assigned to be 9-cis by resonance Raman spectroscopy. Different from the previous reports, the configuration of this α-carotene in dissociated state was determined to be all-trans. Besides this carotene, chlorophyll a was also found in this complex. It was shown that the molecular ratios of chlorophylla, cis and all-trans-α-carotene to Cyt f in this complex were 1.2, 0.7 and 0.2, respectively.