ISOLATION AND CHARACTERIZATION OF NATIVE PIGMENT‐PROTEIN COMPLEXES FROM TWO EUSTIGMATOPHYCEAE¹

Abstract

ABSTRACT Pigment‐protein complexes were isolated from two species of Eustigmatophyceae, Monodus subterraneus Peterson and Vischeria punctata Vischer, by digitonin treatment followed by density gradient centrifugation. Absorption and fluorescence spectra of the samples were monitored at various steps of preparation, and pigment composition was analyzed by reverse phase HPLC. Although the fluorescence emission spectra were very different in the two species, the absorption spectra were similar, and each exhibited an absorption band with a maximum at 487 nm attributable to violaxanthin and vaucheriaxanthin ester (the molar concentration of these pigments in Monodus was, respectively, 28 and 10 per 100 Chl a). The light‐harvesting role of these xanthophylls was ascertained by fluorescence excitation spectra. The light‐harvesting fractions (LH) collected in the upper part of the gradient were depleted in β‐carotene, whereas their xanthophyll/chlorophyll ratio was almost the same as in whole cells. This is consistent with the presence in these algae of large LH antennae and relatively small core antennae in the photosystems. In Monodus , a polypeptide of 23 kDa, immunologically related to the major LH polypeptide of brown algae, constituted the majority of the LH protein moiety.