title: Determination of the equilibrium constant for the binding of ferricytochrome c to phospholipid vesicles and the effect of binding on the reduction rate of cytochrome c.
abstract: The rate of reduction of cytochrome c by 2-amino-4-hydroxy-6,7-dimethyl-5,6,7,8-tetrahydropteridine was examined as a function of binding to liposomes prepared from mixed soybean phospholipids, asolectin, and from various purified phospholipids. Binding of cytochrome c to asolectin liposomes caused an increase in the rate of reduction by the pteridine derivative from 2900 to 16 000 M-1 x s-1 at pH 7. At low ionic strength (0.003 M) the binding stoichiometry between cytochrome c and asolectin vesicles is 15 +/- 2 phosphospolipid/cytochrome c (mole ratio), determined by monitoring the change in reduction rate of cytochrome c by pteridine as cytochrome c is bound to the vesicles. A stoichiometry of 14 phospholipid/cytochrome c was obtained from gel filtration studies. Equilibrium association constants for the binding of cytochrome c to sites on the asolectin vesicles varies from 2.2 x 10(6) to 1.8 x 10(3) M-1 between 0.02 and 0.10 M ionic strength, respectively. In general, liposomes prepared from purified phospholipids resulted in less binding of cytochrome c per mole of phospholipid and lower reduction rates than those prepared from asolectin.
mesh_terms: D000818:Animals; D002850:Chromatography, Gel; D003574:Cytochrome c Group / Q000378:metabolism*; D004579:Electron Transport; D006736:Horses / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D010084:Oxidation-Reduction; D010743:Phospholipids / Q000378:metabolism*; D011621:Pteridines / Q000494:pharmacology*; D013057:Spectrum Analysis
chemical_list: D003574:Cytochrome c Group; D008081:Liposomes; D010743:Phospholipids; D011621:Pteridines