Electrostatic modulation of the kinetics of electron transfer from cytochrome c to cobalt phenanthroline by binding to lipid bilayers: effects of ionic strength and extent of incorporation of various negatively charged lipids.
The effect of electrostatically binding ferrous cytochrome c to anionic liposomes, composed of dimyristoyl phosphatidylglycerol (DMPG-), dioleoyl phosphatidyl-glycerol (DOPG-), or cardiolipin (CL2-) mixed with varying amounts of egg phosphatidylcholine (PC), on the kinetics of cytochrome oxidation by the positively charged cobalt phenanthroline ion has been measured using stopped-flow spectrophotometry. The rate of electron transfer is enhanced as much as 3000-fold by increasing the number of negatively charged binding sites on the liposome surface, and by as much as 1000-fold by decreasing the ionic strength of the buffer. The sigmoidal shape of the curve of rate constant vs mole percent anionic lipid is consistent with a positively cooperative effect of the negative surface charge. The rate stimulation is greater for DOPG(-)- and CL2(-)-containing liposomes than for DMPG- vesicles; this is most likely due to structural differences in the respective liposomes. The results do not provide any support for a role of structural changes in the bound cytochrome in influencing oxidation kinetics, a possibility suggested by recent spectroscopic measurements, although relatively small conformational effects cannot be completely ruled out.
Cheddar
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University of Arizona, Department of Biochemistry, Tucson 85721.
Tollin
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D000838:Anions; D002308:Cardiolipins / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism*; D004563:Electrochemistry; D004579:Electron Transport; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism*; D050356:Lipid Metabolism; D008081:Liposomes / Q000378:metabolism*; D009942:Organometallic Compounds / Q000378:metabolism*; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D010618:Phenanthrolines / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D010715:Phosphatidylglycerols / Q000378:metabolism
D000838:Anions; D002308:Cardiolipins; D003574:Cytochrome c Group; D008051:Lipid Bilayers; D008081:Liposomes; D009942:Organometallic Compounds; D010618:Phenanthrolines; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; C035551:triphenanthrolinecobalt(III); C051388:1,2-dioleoyl-sn-glycero-3-phosphoglycerol; C002773:dimyristoylphosphatidylglycerol