On the mechanism of ubiquinone mediated photocurrent generation by a reaction center based photocathode.

Upon photoexcitation, the reaction center (RC) pigment-proteins that facilitate natural photosynthesis achieve a metastable separation of electrical charge among the embedded cofactors. Because of the high quantum efficiency of this process, there is a growing interest in their incorporation into biohybrid materials for solar energy conversion, bioelectronics and biosensing. Multiple bioelectrochemical studies have shown that reaction centers from various photosynthetic organisms can be interfaced with diverse electrode materials for the generation of photocurrents, but many mechanistic aspects of native protein functionality in a non-native environment is unknown. In vivo, RC's catalyse ubiquinone-10 reduction, protonation and exchange with other lipid phase ubiquinone-10s via protein-controlled spatial orientation and protein rearrangement. In contrast, the mechanism of ubiquinone-0 reduction, used to facilitate fast RC turnover in an aqueous photoelectrochemical cell (PEC), may not proceed via the same pathway as the native cofactor. In this report we show truncation of the native isoprene tail results in larger RC turnover rates in a PEC despite the removal of the tail's purported role of ubiquinone headgroup orientation and binding. Through the use of reaction centers with single or double mutations, we also show the extent to which two-electron/two-proton ubiquinone chemistry that operates in vivo also underpins the ubiquinone-0 reduction by surface-adsorbed RCs in a PEC. This reveals that only the ubiquinone headgroup is critical to the fast turnover of the RC in a PEC and provides insight into design principles for the development of new biophotovoltaic cells and biosensors.

Novel solid self-emulsifying drug delivery system of coenzyme Q10 with improved photochemical and pharmacokinetic behaviors.

The present study was undertaken to develop a solid self-emulsifying drug delivery system of coenzyme Q(10) (CoQ(10)/s-SEDDS) with high photostability and oral bioavailability. The CoQ(10)/s-SEDDS was prepared by spray-drying an emulsion preconcentrate containing CoQ(10), medium-chain triglyceride, sucrose ester of fatty acid, and hydroxypropyl cellulose, and its physicochemical, photochemical, and pharmacokinetic properties were evaluated. The CoQ(10)/s-SEDDS powder with a diameter of ca. 15 µm was obtained by spray-drying, in which the CoQ(10) was mostly amorphized. The CoQ(10)/s-SEDDS exhibited immediate self-emulsification when introduced to aqueous media under gentle agitation, forming uniform fine droplets with a mean diameter of ca. 280 nm. There was marked generation of reactive oxygen species, in particular superoxide, from CoQ(10) exposed to simulated sunlight (250W/m(2)), suggesting potent photoreactivity. Nano-emulsified solution of CoQ(10) under light exposure underwent photodegradation with 22-fold higher degradation kinetics than crystalline CoQ(10), although the CoQ(10)/s-SEDDS was less photoreactive. After the oral administration of CoQ(10)/s-SEDDS (100 mg-CoQ(10)/kg) in rats, enhanced exposure of CoQ(10) was observed with increases in both C(max) and AUC of ca. 5-fold in comparison with those of orally administered crystalline CoQ(10). From the improved physicochemical and pharmacokinetic data, the s-SEDDS approach upon spray-drying might be a suitable dosage option for enhancing nutraceutical and pharmaceutical values of CoQ(10).

Photolabile ubiquinone analogues for identification and characterization of quinone binding sites in proteins.

Quinones are essential components in most cell and organelle bioenergetic processes both for direct electron and/or proton transfer reactions but also as means to regulate various bioenergetic processes by sensing cell redox states. To understand how quinones interact with proteins, it is important to have tools for identifying and characterizing quinone binding sites. In this work three different photo-reactive azidoquinones were synthesized, two of which are novel compounds, and the methods of synthesis was improved. The reactivity of the azidoquinones was first tested with model peptides, and the adducts formed were analyzed by mass spectrometry. The added mass detected was that of the respective azidoquinone minus N(2). Subsequently, the biological activity of the three azidoquinones was assessed, using three enzyme systems of different complexity, and the ability of the compounds to inactivate the enzymes upon illumination with long wavelength UV light was investigated. The soluble flavodoxin-like protein WrbA could only use two of the azidoquinones as substrates, whereas respiratory chain Complexes I and II could utilize all three compounds as electron acceptors. Complex II, purified in detergent, was very sensitive to illumination also in the absence of azidoquinones, making the 'therapeutic window' in that enzyme rather narrow. In membrane bound Complex I, only two of the compounds inactivated the enzyme, whereas illumination in the presence of the third compound left enzyme activity essentially unchanged. Since unspecific labeling should be equally effective for all the compounds, this demonstrates that the observed inactivation is indeed caused by specific labeling.

High-sensitive determination of coenzyme Q(10) in iodinate-beta-cyclodextrin medium by inclusion reaction and catalytic polarography.

A novel polarographic method for the determination of coenzyme Q(10) in beta-cyclodextrin (beta-CD) and iodinate system is proposed. The stability of coenzyme Q(10) to light was improved by the formation of coenzyme Q(10)-beta-CD inclusion complex. In addition, the sensitivity for the determination of coenzyme Q(10) was enhanced by both the formation and the polarographic catalytic wave of the inclusion complex in the presence of iodinate. In 0.1 mol/L HAc-NaAc (pH 4.7)-5.0 x 10(-5) mol/L beta-CD-1.2 x 10(-3) mol/L potassium iodinate-ethanol/water (60:40, v/v) medium, coenzyme Q(10)-beta-CD inclusion complex yielded a sensitive association/parallel catalytic wave. The second-order derivative peak current of the catalytic wave was proportional to coenzyme Q(10) concentration in the range of 6.0 x 10(-8)-2.5 x 10(-7) mol/L, and the detection limit was 1.0 x 10(-8) mol/L. The proposed method has high analytical sensitivity and is allowed to determine coenzyme Q(10) under light.

Antioxidantes y envejecimiento cutáneo / Antioxodants and cutaneous aging

Las formulaciones disponibles actualmente para uso dermatológico, basadas en sustancias antioxidantes tales como vitaminas C y E, entre otras, abundan con promesas de revertir el envejecimiento cutáneo. En el presente trabajo se realiza una revisión de los sistemas antioxidantes cutáneos, de la relación entre envejecimiento y daño oxidativo, así como de la evidencia disponible en cuanto al tratamiento con antioxidantes. La intención de este artículo es que el dermatólogo comprenda las bases fisiológicas de acción de los antioxidantes, para poder juzgar su utilidad con una mirada crítica (AU)

Reduction of 1,4-quinone and ubiquinones by hydrogen atom transfer under UVA irradiation.

1,4-Benzoquinone, coenzyme Q0 and Q10 were reacted with a series of hydrogen donors in the ESR cavity in the presence or absence of UVA irradiation. The signals of the radicals generated from the hydrogen donors or of those of the semiquinones were detected. The reaction mechanism was interpreted by a hydrogen atom transfer instead of the usual electron transfer mechanism on the basis of the redox potentials of the reactants and the Marcus theory. The hydrogen atom transfer is explained by the excited triplet state of quinones, which, on the basis of quantum mechanic calculations, may be reached even under visible light. In some cases, hydrogen atom transfer was also observed without irradiation, although to a lesser extent.

Mitochondrial respiratory chain features after gamma-irradiation.

Radiation provokes damage to DNA but also to membrane and protein structure. Radiolysis is a tool used very often in the study of free radical biological effects and of scavenger molecules effectiveness. Nitroimidazoles have been demonstrated to enhance the radiation effects on biological structures. The studies we have performed on isolated mitochondria irradiated, with and without nitroimidazoles, at a radiation dose equal to LD90, indicate that this treatment is not able to affect the structural and functional features investigated (ubiquinone-10, fatty acids, respiratory cytochrome levels or membrane fluidity and respiratory enzymatic activities), suggesting that an involvement of such externally produced radicals on membrane damage is unlikely. Moreover it was ascertained that the mitochondrial redox activities do not take part into the intracellular nitroimidazole reduction.

Recovery of antioxidants and reduction in lipid hydroperoxides in murine epidermis and dermis after acute ultraviolet radiation exposure.

In previous studies we have found that a single acute dose of ultraviolet radiation to murine skin causes a large degree of destruction of enzymic and non-enzymic antioxidants immediately after irradiation. In the present study, we wished to elucidate the recovery of antioxidants after a single dose of ultraviolet (UV) radiation. We measured antioxidants and lipid hydroperoxides (as a marker of membrane damage) in murine epidermis and the dermis at 0, 3, 12, 24, 72 and 120 h after exposure to UV radiation (25 J/cm2, UVA+UVB). Lipid hydroperoxides showed the highest values immediately after UV exposure and returned to control values within 24 h in both epidermis and dermis. The activities of catalase, glutathione peroxidase and glutathione reductase showed the lowest activities immediately after UV exposure; superoxide dismutase activities reached a minimum at 3 h postexposure. The pattern of recovery was different for each enzyme and for epidermis and dermis. The activities of superoxide dismutase and catalase decreased remarkably and recovered slowly. Superoxide dismutase in the dermis recovered full activity by 120 h and in the epidermis by 12 h. Catalase activity in both epidermis and dermis had returned to only 50% of control activity at 120 h, although the epidermis showed a temporary increase (to 93%) at 24 h. Glutathione peroxidase and glutathione reductase were slightly decreased immediately after irradiation, recovered to 100% at 3 h and then increased to 200-250% in both the epidermis and the dermis at various times; values had returned to 100% in epidermis by 120 h but remained elevated in dermis.(ABSTRACT TRUNCATED AT 250 WORDS)

Destruction of vitamin K1 of cultured carrot cells by ultraviolet radiation and its effect on plasma membrane electron transport reactions.

The effect of ultraviolet radiation on plasma membrane electron transport reactions was studied in cultured carrot cells. It was found that a 90 min treatment inhibited transmembrane hexacyanoferrate reduction greater than 50%. Extraction of lipophilic quinones from irradiated cells showed that vitamin K1 and coenzyme Q were totally destroyed, while control unirradiated cells showed the presence of 0.4 mumole vitamin K1 g dry wt.-1. The addition of exogenous vitamin K1 in concentrations of 1-10 microM partially restored plasma membrane electron transport with impermeable hexacyanoferrate as the electron acceptor. Total restoration of activity was given by growing irradiated cells in vitamin K1 supplemented growth media for 6 days. This shows that vitamin K1 may function as a member of the transplasma membrane electron transport chain in cultured carrot cells.

Photostability of solid-state ubidecarenone at ordinary and elevated temperatures under exaggerated UV irradiation.

The photostability of ubidecarenone was investigated. Two irradiation apparatus, a grating monochromator and a high-pressure mercury vapor lamp, were employed at ordinary and elevated temperatures. Both physicochemical and chemical stabilities were significantly affected by irradiation wavelength, with UV light causing the greatest changes. The degree of degradation was a function of the light absorption properties of the substrate and markedly increased when the absorption became greater than 30%. The photolytic degradation followed apparent first-order kinetics at all wavelengths and was promoted with temperature elevation. The Arrhenius plot gave an activation energy in the solid state different from that in the liquid state. These activation energies linearly decreased with increasing intensity of UV light.