EVIDENCE FOR A COMMON EVOLUTIONARY ORIGIN OF LIGHT‐HARVESTING FUCOXANTHIN CHLOROPHYLL a/c‐PROTEIN COMPLEXES OF PAVLOVA GYRANS (PRYMNESIOPHYCEAE) AND PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

Abstract

ABSTRACTA fucoxanthin‐chlorophyll a/c‐protein complex has been isolated from the prymnesiophyte Pavlova gyrans. Thylakoid membranes were treated with the mild anionic detergent sodium taurodeoxycholate followed by sucrose density gradient centrifugation. The brown fraction produced by this procedure was treated with Triton X‐100 followed by a second sucrose density gradient centrifugation. A brown fraction isolated from this gradient was shown to be a light‐harvesting complex nearly identical to that which is present in the diatom Phaeodactylum tricornutum. The complexes from the two organisms have nearly identical absorption and flourescence spectra, both complexes contain fucoxanthin and two other carotenoids, both contain four polypeptides of similar molecular weights, and polypeptides from both complexes cross react with antibodies raised to polypeptides of the Phaeodactylum tricornutum complex. Results suggest a common evolutionary origin for these light‐harvesting complexes, in apparent contrast to the great differences in cell structure between prymnesiophytes and diatoms.