Analysis of photoreceptor proteins of microorganisms by gradient gel electrophoresis and other biochemical separation...

Photoreceptor proteins for photoorientation in microorganisms are usually membrane bound and can be isolated by standard biochemical methods. Three examples are shown: the flagellates Euglena gracilis, Peridinum gatunense and the slime mold Dictyostelium discoideum. The photoreceptor of Euglena is attached to the basis of the flagellum and is composed of at least four chromoproteins which can be separated by gradient sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) fast protein liquid chromatography (FPLC) and isoelectric focusing (IEF); it contains pterins and a flavin as chromophoric groups. The photoreceptor of Peridinium absorbs in the red wavelength band. Though not yet identified in detail, multiple receptors are probably involved, as indicated by fluorescence spectroscopy. Dictyostelium shows positive and negative phototaxis in its amoebal form and exclusively positive phototaxis in its pseudoplasmodial form. It is still open to discussion whether the two stages use separate photoreceptors. From amoebae two photoreceptor pigments have been isolated, showing an absorption which resembles the action spectrum, one membrane bound with a molecular mass of 45 kDa and one cytoplasmic fraction with a molecular mass of 27 kDa.