Superoxide anion permeability of phospholipid membranes and chloroplast thylakoids.
The permeability of phospholipid membranes to the superoxide anion (O-2) was determined using soybean phospholipid vesicles containing FMN in the internal space. The efflux of O-2 generated by the illumination of FMN was so slow that more than 90% of the radicals were spontaneously disproportionated within the vesicles before they could react with cytochrome c at the membrane exterior. The amount of diffused O-2 was proportional to the intravesicular concentration of O-2 over a range from 1 to 10 microM which was deduced from its disproportionation rate. The permeability coefficient of the phospholipid bilayer for O-2 was estimated to be 2.1 X 10(-6) cm s-1 at pH 7.3 and 25 degrees C. Superoxide dismutase trapped inside vesicles was not reactive with extravesicular O-2 unless Triton X-100 was added. O-2 generated outside spinach chloroplast thylakoids did not interact with superoxide dismutase or cytochrome c which had been enclosed in the thylakoids. Thus, chloroplast thylakoids also showed little permeability to O-2.
D002736:Chloroplasts / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism; D005486:Flavin Mononucleotide / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism*; D007700:Kinetics; D008081:Liposomes; D010101:Oxygen Consumption; D010539:Permeability; D010743:Phospholipids / Q000378:metabolism; D010944:Plants / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*
D003574:Cytochrome c Group; D008081:Liposomes; D010743:Phospholipids; D013481:Superoxides; D005486:Flavin Mononucleotide; D013482:Superoxide Dismutase