Biochemical and spectroscopic characterization of the putative photoreceptor for phototaxis in amoebae of the cellular slime mould Dictyostelium discoideum.

Using sucrose gradient centrifugation, anion exchange chromatography on a SMART system, isoelectric focusing (IEF) and sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS PAGE), a 45.5 kDa membrane protein was isolated from amoebae of the cellular slime mould Dictyostelium discoideum. The absorption spectrum of the isolated protein corresponds well with the action spectrum for the photoaccumulation of the amoebae of Dictyostelium discoideum showing a major peak between 405 and 412 nm and some minor peaks between 500 and 600 nm. The remarkable similarity of the two spectra leads to the hypothesis that the isolated protein-pigment complex may serve as a photoreceptor for amoebal phototaxis.