Isolation and characterization of three membranebound chlorophyll-protein complexes from four dinoflagellate species

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Abstract
Employing discontinuous sucrose density gradient centrifugation ofn-dodecyl β-d-maltoside-solubilized thylakoid membranes, three chlorophyll (Chl)-protein complexes containing Chla, Chlc2and peridinin in different proportions, were isolated from the dinoflagellatesSymbiodinium microadriaticum, S. kawagutii, S. pilosumandHeterocapsa pygmaea. InS. microadriaticum, the first complex, containing 13% of the total cellular Chla, and minor quantities of Chlc2and peridinin, is associated with polypeptides with apparent molecular mass (Mr) of 8-9 kDa, and demonstrated inefficient energy transfer from the accessory pigments to Chla. The second complex contains Chla, Chlc2and peridinin in a molar ratio of 1:1:2, associated with two apoproteins ofMr19-20 kDa, and comprises 45%, 75% and 70%, respectively, of the cellular Chla, Chlc2and peridinin. The efficient energy transfer from Chlc2and peridinin to Chlain this complex is supportive of a light-harvesting function. This Chla-c2- peridin-protein complex represents the major light-harvesting complex in dinoflagellates. The third complex obtained contains 12% of the cellular Chla, and appears to be the core of photosystem I, associated with a light-harvesting complex. This complex is spectroscopically similar to analogous preparations from different taxonomic groups, but demonstrates a unique apoprotein composition. Antibodies against the water-soluble peridinin-Chla-protein (sPCP) light-harvesting complexes failed to cross-react with any of the thylakoid-associated complexes, as did antibodies against Chla-c-fucoxanthin apoprotein (from diatoms). Antibodies against the P700apoprotein of plants did not cross-react with the photosystem I complex. Similar results were observed in the other dinoflagellates.