Succinate: quinone oxidoreductases: Variations on a conserved theme

Procaryotic complex I (NDH-1), an overview.

Quinones in biology: functions in electron transfer and oxygen activation

On the universal core of bioenergetics

Isoprenoid quinones as biomarkers of microbial populations in the environment.

Redox components bound with chromatophores of Rhodospirillum rubrum, and pure samples of ubiquinone-10 and rhodoquinone were studied polarographically at 24 degrees. In a mixture of ethanol and water (4 : 1, v/v) at pH 7, ubiquinone-10 and rhodoquinone had half-wave potentials (E1/2) OF +43 MV and -63 mV, respectively. For both quinones, values of the electron transfer number (n) were 2 , and plots of E1/2 versus pH formed straight lines with slopes of -30 mV/pH in the neutral pH range; thus, values of the proton transfer number (n-a) were estimated to be 1 for both quinones. When bound with chromatophores, ubiquinone-10 and rhodoquinone had E1/2 values of +50 mV (n=2) and -30 mV (n=2), respectively, at pH 7. Values of (n-a) were estimated to be 1 for ubiquinone-10 and 2 for rhodoquinone. A component (POC-170) thought to be one of the active center bacteriochlorophylls (Liac-890) was characterized; it has E1/2 value of -170 mV at pH 7 and its oxidation-reduction is possibly brought about by dehydrogenation-hydrogenation. Conceivably, the oxidation-reduction sites of ubiquinone-10, rhodoquinone and POC-170 partly, if not all, exist on the surface of chromatophore membrane or project outside the membrane, because of their accessibility to the polarographic electrode.

Polarographic studies on ubiquinone-10 and rhodoquinone bound with chromatophores from Rhodospirillum rubrum.

Ubiquinone-10 solubilized in an aqueous solution containing sodium dodecyl sulfate as an anionic surfactant was polarographically investigated Ubiquinone-10 solubilized in micelles shows a well-defined, diffusion-controlled, pH-dependent wave Diffusion coefficient and apparent particles radii were calculated The surfactant concentration dependence of the diffusion coefficient and of the apparent particle radii was also determined

Polarographic Reduction of Ubiquinone-10 Solubilized in Micelles

Polarographic studies on oxidation-reduction components bound with chromatophores from Rhodospirillum rubrum were carried out at 24 degrees. 1. Using a carbon-paste electrode as the working electrode, polarographic waves characteristic of oxidation-reduction components were observed in the presence, but not in the absence of Triton X-100; these waves were therefore measured in the presence of the detergent. 2. At least two kinds of oxidation-reduction components were detectable, having different half-wave potentials (E1/2); at pH 7, one had an E1/2 value of +275 mV (POC+275) and the other had a value of +60 mV (POC+60). 3. POC+275 was reduced by succinate and by NADH. Both reductions were almost completely inhibited by antimycin A, which hardly affected the reductions of ubiquinone-10 by succinate and by NADH. Most POC+275 molecules were not reduced by the substrates when quinones were extracted from the chromatophores, and the reductions were mostly restored when ubiquinone-10 was re-added. This indicates that POC+275 is functional between ubiquinone-10 and cytochrome c2 in the electron transport system. 4. POC+60 was reduced by succinate, but hardly at all by NADH. The reduction of POC+60 was not influenced either by the addition of antimycin A or by the extraction of quinones. This suggests that POC+60 is functional in the process from succinate dehydrogenase [EC 1.3.99.1] to ubiquinone-10 in the electron transport system. 5. Of the POC+275 reducible by dithionite, approximately 70% could be reduced in the absence of Triton X-100, provided that the potential of the working electrode immersed in chromatophore suspensions was set at potentials of 0 mV or lower and that the electrochemical reaction was carried out at pH 7.5. When the potential of the electrode was set at +50 mV (the same as the E1/2 value of ubiquinone-10 bound with chromatophores), and the suspension was allowed to stand for various lengths in the presence of the detergent, it was found that approximately half of the electrochemically reducible POC+275 was rapidly reduced, followed by a slow reduction. The discrepancy in the oxidation-reduction equilibrium on the basis of the E1/2 values of ubiquinone-10 and POC+275 is discussed.

Polarographic studies in presence of Triton X-100 on oxidation-reduction components bound with chromatophores from Rhodospirillum rubrum.

Anodic Oxidation of N , N -Dimethyl- p -phenylenediamine with Sodium Sulfite

When the photosynthetic organs, chromatophores, were electrolyzed under light by using some noble metal electrodes, the observed photocurrent depended both on electrode potential and on the concentration of chromatophores. The photocurrent was enhanced by addition of PMS, Methoxy PMS or DCPI to the chromatophore suspension. The mechanism of the photocurrent is also discussed briefly.

Masaya Tanaka

Papers

Polarographic studies on ubiquinone-10 and rhodoquinone bound with chromatophores from Rhodospirillum rubrum.

Polarographic Reduction of Ubiquinone-10 Solubilized in Micelles

Polarographic studies in presence of Triton X-100 on oxidation-reduction components bound with chromatophores from Rhodospirillum rubrum.

Anodic Oxidation of N , N -Dimethyl- p -phenylenediamine with Sodium Sulfite

Photoelectrochemical behavior of chromatophores at some noble metal electrodes.