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 subunit 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 dinoflagellate Rubisco was identified on native polyacrylamide gels by autoradiographic detection of the stable Rubisco-[2'-14C]-2-carboxy-D-arabinitol 1,5-bisphosphate complex. The antibody to the Symbiodinium sp. large subunit cross reacts with both the Rhodospirillum rubrum and Rhodobacter sphaeroides Form II enzyme whereas antibodies to the R. rubrum 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 relation. The lack of inhibition of the dinoflagellate Rubisco by 6-phosphogluconate is consistent with this structure.