Purification and Characterization of a Light-Harvesting Chlorophyll-Protein Complex from the Marine EustigmatophyteNannochloropsissp.

摘要

Light-harvesting chlorophyll-protein was purified from thylakoid membranes of the marine unicellular algaNannochloropsissp. (Eustigmatophyceae), which contains neither chlorophyllbnor chlorophyllc. Solubilization of thylakoid membranes with octyl-β-D-glucopyranoside or with digitonin followed by separation on sucrose density gradient yielded a chlorophyll-protein complex composed of an apoprotein of 26 kDa and an average of 9 chlorophyllaand 4 violaxanthin molecules per apoprotein. Excitation spectra of chlorophyllafluorescence for the algal thylakoid membranes indicated energy transfer from the xanthophylls; however, any attempt to solubilize the membranes greatly decreased energy transfer which was further reduced as the purification proceeded. The 26 kDa polypeptide of the isolated light-harvesting complex did not cross-react with polyclonal antibodies raised against analogous proteins from higher plants and chlorophylla/calga. The N-terminus amino acid sequence of the apoprotein shows significant structural similarity to the N-termini of the mature light harvesting fucoxanthin, chlorophylla/cproteins from the diatomPhaeodactylum tricornutum, but not with the N-termini of light-harvesting proteins from chlorophylla/bcontaining organisms