CHARACTERIZATION OF THE LIGHT-HARVESTING PROTEINS OF THE CHROMOPHYTICALGA, OLISTHODISCUS-LUTEUS (HETEROSIGMA-CARTERAE)

The light-harvesting complexes (LHC) of the unicellular marine chromop hyte, Olisthodiscus luteus (Heterosigma carterae), were fractionated b y sucrose-density gradient centrifugation following digitonin solubili zation, and by non-denaturing SDS-PAGE. The sucrose gradient allowed f or the isolation of a major light-harvesting complex fraction, contain ing approximately 53% of the total chlorophyll, the majority of the ch lorophyll c and a single polypeptide of 19.5 kDa. Up to 12 different l ight-harvesting polypeptides were detected in thylakoids and in the lo wer Photosystem I (PS I) related fractions using polyclonal antibodies specific for barley light-harvesting complexes or a diatom fucoxanthi n-Chl a/c complex. The non-denaturing gel system of Allen and Staeheli n (Anal. Biochem. 194 (1991) 214-222) allowed the resolution of a numb er of large pigment-protein complexes, an improvement over previous el ectrophoretic separation methods applied to the chromophytic algae. Di fferences among the light-harvesting polypeptides in apparent molecula r mass, immunological cross-reactivity and distribution among differen t pigment-protein complexes suggest that this protein family may be as complex as the family of chlorophyll a/b light-harvesting polypeptide s in green algae and higher plants.