Kondrashin Aa

Generation of electric current by chromatophores of Rhodospirillum rubrum and reconstitution of electrogenic function in subchromatophore pigment-protein complexes

Lipoprotein complexes, containing (1) bacteriochlorophyll reaction centers, (2) bacteriochlorophyll light-harvesting antenna or (3) both reaction centers and antenna, have been isolated from chromatophores of non-sulphur purple bacteria Rhodospirillum rubrum by detergent treatments. The method of reconstituting the proteoliposomes containing these complexes is described. Being associtated with planas azolectin membrane, ptoteoliposomes as well as intact chromatophores were found to generate a light-dependent transmembrane electric potential difference measured by Ag/AgC1 electrodes and voltmeter. The direction of the electric field inproteoliposomes can be regulated by the addition of antenna complexes to the reconstitution mixture. The reaction center complex proteoliposomes generate an electric field of a direction opposite to that in chromatophores, whereas proteoliposomes containing reaction center complexes and a sufficient amount of antenna complexes produce a potential difference as in chromatophores. ATP and inorganic pyrophosphate, besides light, were shown to be usable as energy sources for electric generation in chromatophores associated with planar membrane.

Generation of electric potential by reaction center complexes from Rhodospirillum rubrum

Several lines of indirect evidence indicate that the electrochemical H’ potential is produced by the lightdependent cyclic electron transfer in chromatophores and intact bacterial cells [l-4] , as was originally postulated by Mitchell [ 51. In this paper, data on the direct measurement of electric current generation by bacteriochlorophyll reaction center complexes, isolated from R. rubrum chromatophores, is reported. A method of reconstitution of the reaction center complex-containing proteoliposomes and their association with planar phospholipid membranes was elaborated. Formation of light-induced electric potential difference by the proteoliposomes was demonstrated by the conventional voltmeter techniques as well as by a phenyldicarbaundecaborane (PCB-) probe. The photoelectric effect was shown to increase on addition of TMPD or cytochrome c in combination with CoQ or vitamin Ka , and to decrease on addition of ferricyanide, o-phenanthroline and a protonophorous uncoupler.

Charge transfer between water and octane phases by soluble mitochondrial ATPase (F1), bacteriorhodopsin and respiratory chain enzymes

According to Mitchell’s chemiosmotic theory of energy coupling, there are special enzymic systems carrying out translocation of electrons or protons across biological membranes [ 1 ] . Such a translocation should include the stages of electron (proton) transfer through a water-lipid interface, the processes being catalyzed (a) by certain enzymes operating in the energy coupling sites of the respiratory and photosynthetic redox chains, and (b) by H+-ATPase. In this paper, we shall report a method of investigation of the enzyme-mediated charge transfer across a water-lipid interface. The method consists in the measurement of the Volta potential difference between an octane and water solution, containing the enzyme system studied. Positive charging of the octane phase was found to be induced by soluble mitochondrial ATPase (Fr) in an ATP-dependent fashion, or by bacteriorhodopsin from Halobacterium halobium in a light-dependent fashion. In both cases, a lipid-soluble proton acceptor proved to be necessary. Cytochrome oxidase and succinate-cytochrome c-reductase were shown to carry out negative charging of octane if a lipid-soluble electron acceptor and water soluble elec-

Functional role of soluble mitochondrial ATPase subunits

A preparation of soluble mitochondrial ATPase (coupling factor F1) containing no γ and δ minor subunits has been isolated. The minor-subunits-deficient F1 was found to be competent in ATP hydrolysis. However, it did not demonstrate a “coupling” effect in EDTA-submitochondrial particles. A portion of the ATPase activity of EDTA particles, stimulated by the minor-subunits-deficient F1, was insensitive to oligomycin. ATPase activity of Na+-particles was changed only slightly by this F1. It is suggested that γ and δ subunits are necessary to form specific contacts between the F1 molecule and components of the mitochrondrial membrane.