BIOCHEMICAL AND SPECTROSCOPIC CHARACTERIZATION OF THE PUTATIVE PHOTORECEPTOR FOR PHOTOTAXIS IN AMEBAS OF THE CELLULAR SLIME-MOLD DICTYOSTELIUM-DISCOIDEUM

Using sucrose gradient centrifugation, anion exchange chromatography o n a SMART system, isoelectric focusing (IEF) and sodium dodecylsulphat e polyacrylamide gel electrophoresis (SDS PAGE), a 45.5 kDa membrane p rotein was isolated from amoebae of the cellular slime mould Dictyoste lium discoideum. The absorption spectrum of the isolated protein corre sponds well with the action spectrum for the photoaccumulation of the amoebae of Dictyostelium discoideum showing a major peak between 405 a nd 412 nm and some minor peaks between 500 and 600 nm. The remarkable similarity of the two spectra leads to the hypothesis that the isolate d protein-pigment complex may serve as a photoreceptor for amoebal pho totaxis.