EVIDENCE THAT SOME DINOFLAGELLATES CONTAIN A RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE RELATED TO THAT OF THE ALPHA-PROTEOBACTERIA

The ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) large su bunit from several dinoflagellates has a structure similar to that of the Form II enzyme from Rhodospirillum and Rhodobacter species rather than the Form I Rubisco of eukaryotic algae and higher plants. The din oflagellate Rubisco was identified on native polyacrylamide gels by au toradiographic detection of the stable Rubisco-[2'-C-14]-2-carboxy-D-a rabinitol 1,5-bisphosphate complex. The antibody to the Symbiodinium s p. large subunit cross reacts with both the Rhodospirillum rubrum and Rhodobacter sphaeroides Form II enzyme whereas antibodies to the R. ru brum Rubisco cross react with a range of dinoflagellate Rubisco large subunits. The N-terminal amino acid sequence of the large subunit from both Symbiodinium sp. and Amphidinium carterae confirmed this relatio n. The lack of inhibition of the dinoflagellate Rubisco by 6-phosphogl uconate is consistent with this structure.