A rapid, simple method for the isolation and characterization of the photoreceptor of Dictyostelium discoideum amoebae.

A membrane-bound 45.5 kDa protein has been isolated from Dictyostelium discoideum amoebae. It shows an absorption spectrum, which closely resembles the action spectrum for amoebal phototaxis, leading to the conclusion that this protein might play an important role in the photoreception of Dictyostelium amoebae. For further characterization we employed phase partition in an aqueous polymer two-phase system, which was developed by Widell and Larsson for the separation of plasma membrane proteins of higher plants. This method clearly shows that the 45.5 kDa protein is a plasma membrane protein and not an intracellular protein. Furthermore, by using phase systems with increasing polymer concentrations, this simple and rapid purification of plasma membrane proteins allowed us to isolate the putative photoreceptor in one single step. Compared to standard biochemical methods phase partition provides an enormous facilitation of the isolation of D. discoideum membrane proteins.