RESUMO
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.
Assuntos
Dictyostelium/química , Proteínas de Membrana/química , Animais , Movimento Celular , Dictyostelium/fisiologia , Luz , Proteínas de Membrana/fisiologia , Células Fotorreceptoras de Invertebrados/fisiologia , EspectrofotometriaRESUMO
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.
Assuntos
Membrana Celular/química , Dictyostelium/ultraestrutura , Proteínas de Membrana/isolamento & purificação , Células Fotorreceptoras de Invertebrados , Animais , Fracionamento Celular , Membrana Celular/ultraestrutura , Dextranos , Eletroforese em Gel de Poliacrilamida , PolietilenoglicóisRESUMO
Three proteins containing 138 amino acids (psaD protein), 80 amino acids (psaC protein) and 66 amino acids (psaE protein) of the photosystem I (PS I) complex of the cyanobacterium Fremyella diplosiphon (Calothrix sp PCC 7601) were isolated and sequenced. Comparison with previously known sequences showed a close relationship to homologous proteins of Nostoc, another filamentous cyanobacterium.
