title: Quantization of membrane potential generation by cytochrome c oxidase in small vesicles.
abstract: Proteoliposomes incorporating cytochrome c oxidase have been prepared by the cholate dialysis method and by sonication. Sonication produces multilamellar vesicles heterogeneous in size in contrast to a more uniform preparation of unilamellar vesicles produced by the dialysis procedure. Respiratory control in both preparations ranges between 4 and 8. From an electron microscopic analysis of proteoliposome size, the average electrical capacitance/vesicle for the dialyzed and sonicated preparations is calculated as 15 X 10(-18) F and 130 X 10(-18) F, respectively. These capacitance values would lead to a quantization of membrane potential generation by the enzyme at 77 mV/turnover for the dialyzed preparation and 9 mV/turnover for sonicated vesicles. It is argued that these differences can explain the dependence of H+ translocation on the number of turnovers of cytochrome c oxidase in dialyzed preparations in contrast to the lack of dependence on number of turnovers in sonicated preparations.
authors.forename: J M
authors.initials: JM
authors.lastname: Wrigglesworth
mesh_terms: D004553:Electric Conductivity; D003576:Electron Transport Complex IV / Q000502:physiology*; D005614:Freeze Fracturing; D008081:Liposomes / Q000378:metabolism; D008564:Membrane Potentials; D008565:Membrane Proteins; D008854:Microscopy, Electron; D010316:Particle Size; D011522:Protons; D013010:Sonication
chemical_list: D008081:Liposomes; D008565:Membrane Proteins; D011522:Protons; D003576:Electron Transport Complex IV