Characterization of the light harvesting proteins of the chromophytic alga, Olisthodiscus luteus ( Heterosigma carterae)

Abstract

The light-harvesting complexes (LHC) of the unicellular marine chromophyte, Olisthodiscus luteus ( Heterosigma carterae), were fractionated by sucrose-density gradient centrifugation following digitonin solubilization, and by non-denaturing SDS-PAGE. The sucrose gradient allowed for the isolation of a major light-harvesting complex fraction, containing approximately 53% of the total chlorophyll, the majority of the chlorophyll c and a single polypeptide of 19.5 kDa. Up to 12 different light-harvesting polypeptides were detected in thylakoids and in the lower Photosystem I (PS I) related fractions using polyclonal antibodies specific for barley light-harvesting complexes or a diatom fucoxanthin-Chl a c complex. The non-denaturing gel system of Allen and Staehelin (Anal. Biochem. 194 (1991) 214–222) allowed the resolution of a number of large pigment-protein complexes, an improvement over previous electrophoretic separation methods applied to the chromophytic algae. Differences among the light-harvesting polypeptides in apparent molecular mass, immunological cross-reactivity and distribution among different pigment-protein complexes suggest that this protein family may be as complex as the family of chlorophyll a b light-harvesting polypeptides in green algae and higher plants.