Assuntos
Alanina/genética , Álcool Desidrogenase/genética , Isoenzimas/genética , Leucina/química , Mutagênese Sítio-Dirigida , Álcool Desidrogenase/biossíntese , Sítios de Ligação , Escherichia coli , Humanos , Isoenzimas/biossíntese , Cinética , Leucina/genética , Proteínas Recombinantes/biossíntese , Especificidade por SubstratoRESUMO
The spin-label 5-4',4'-dimethyloxazolidinyl-N-oxy stearate (5-doxyl-stearate) exists in a viscous environment when it is incorporated into bleached rod outer segment membranes (ROSM). Addition of the cyclohexyl ring moiety of retinal to ROSM produced a large increase in intramembrane fluidity. A decrease in both the order parameter S (from 0.5 to 0.14) and the rotational correlation time (from 4.0 to 2.0 nsec) gives an estimate of the magnitude of change. Other ring analogs produced similar fluidity changes. The extent of their action depended on their structural similarity to the cyclohexyl of retinal. The pH range in which the cyclohexyl ring produced the increase in ROSM fluidity was 6.8-9.5.
Assuntos
Células Fotorreceptoras/fisiologia , Retinaldeído/fisiologia , Retinoides/fisiologia , Segmento Externo da Célula Bastonete/fisiologia , Animais , Bovinos , Fluidez de Membrana , Lipídeos de Membrana/fisiologia , Retinaldeído/análogos & derivados , Marcadores de Spin , Relação Estrutura-AtividadeRESUMO
Pheomelanin, the red-brown polymeric pigment in the skin and hair of red-headed humans, is composed of a protein fraction covalently bound to a colored chromophore. Photolysis of aerated aqueous phemelanin solutions, isolated from human red hair, results in destruction of the chromophore and liberation of the peptide fraction. The rate of photolysis depends on the pH and the concentration of both pigment and oxygen and is slightly inhibited by the enzyme superoxide dismutase (superoxide:superoxide oxidoreductase EC 1.15.1.1). Pheomelanin photolyzed in the presence of nitroblue tetrazolium results in the formation of a blue diformazan, whether or not oxygen is present. Superoxide dismutase inhibits the aerobic photoreduction of nitroblue tetrazolium whereas, in the absence of oxygen, no inhibition is observed. These experiments strongly suggest the involvement of superoxide in the aerobic photolysis of pheomelanin and point out a possible mechanism for ultraviolet-induced cell damage in redheads.