Monique Gareil

Homogeneous vs. heterogeneous electron transfer in electrochemical reactions: Application to the electrohydrogenation of anthracene and related reactions

Abstract As shown in section (I) summarizing the present state of knowledge in the field, the ECE-DISP problem is an important one in a number of organic and inorganic multi-electron electrochemical reactions. Several routes can be followed to approach it. One is the use of classical electrochemical techniques such as linear sweep voltammetry, cyclic voltammetry and double-potential-step chronoamperometry. This is illustrated by the investigation of the reduction of anthracene in dimethylformamide in the presence of phenol. Contrary to recent contentions, this reaction is shown to follow a “DISP1” limiting mechanism which involves the protonation of the anion radical as the rate-determining step followed by homogeneous electron transfer between the anion radical and the protonated anion radical, yielding the monohydrogenated anion which is itself rapidly and irreversibly protonated into the final dehydrogenated product. The theory, as yet developed, has been extended to make available the formal kinetics corresponding to the other possible limiting mechanisms and to mechanistic situations where the kinetics is not controlled by a single rate-determining step. The mechanism of anthracene reduction has been established by a systematic comparison of the kinetics predicted for these various kinetic situations and the experimental data gathered from linear sweep voltammetry and double-potential-step chronoamperometry in an extended range of substrate and phenol concentrations, sweep rates and inversion times. The danger of using oversimplified reaction-order approaches for unravelling such mechanistic problems is discussed and exemplified.

A multicystatin is induced by drought‐stress in cowpea (Vigna unguiculata (L.) Walp.) leaves

Cystatins are protein inhibitors of cystein proteinases belonging to the papain family. In cowpea, cystatin‐like polypeptides and a cDNA have been identified from seeds and metabolic functions have been attributed to them. This paper describes VuC1, a new cystatin cDNA isolated from cowpea leaves (Vigna unguiculata (L.) Walp.). Sequence analysis revealed a multicystatin structure with two cystatin‐like domains. The recombinant VUC1 protein (rVUC1) was expressed in an heterologous expression system and purified to apparent homogeneity. It appeared to be an efficient inhibitor of papain activity on a chromogenic substrate. Polyclonal antibodies against rVUC1 were obtained. Involvement of the VuC1 cDNA in the cellular response to various abiotic stresses (progressive drought‐stress, dessication and application of exogenous abscissic acid) was studied, using Northern blot and Western blot analysis, in the leaf tissues of cowpea plants corresponding to two cultivars with different capacity to tolerate drought‐stress. Surprisingly, these abiotic stresses induced accumulation of two VuC1‐like messages both translated into VUC1‐like polypeptides. Difference in the transcript accumulation patterns was observed between the two cultivars and related to their respective tolerance level. Presence of multiple cystatin‐like polypeptides and their possible involvement in the control of leaf protein degradation by cysteine proteinases is discussed.

Aspartic protease in leaves of common bean (Phaseolus vulgaris L.) and cowpea (Vigna unguiculata L. Walp): enzymatic activity, gene expression and relation to drought susceptibility.

Four cultivars of related species, common bean and cowpea, which exhibit different degrees of drought resistance, were submitted to water stress by withholding irrigation. Drought induced an increase in endoproteolytic activity, being higher in susceptible cultivars (bean) than in tolerant ones (cowpea). An aspartic protease activity was found to be strongly induced especially in bean. From a cowpea leaf cDNA library, a full length aspartic protease precursor cDNA was obtained. Transcript accumulation in response to water stress indicated that the expression of the gene was constitutive in cowpea and transcriptionally up‐regulated in bean. The results showed that drought‐tolerant and drought‐susceptible bean plants differ regarding aspartic protease precursor gene expression.

Identification of Novel Oxidized Protein Substrates and Physiological Partners of the Mitochondrial ATP-dependent Lon-like Protease Pim1

ATP-dependent proteases are currently emerging as key regulators of mitochondrial functions. Among these proteolytic systems, Pim1, a Lon-like serine protease in Saccharomyces cerevisiae, is involved in the control of selective protein turnover in the mitochondrial matrix. In the absence of Pim1, yeast cells have been shown to accumulate electron-dense inclusion bodies in the matrix space, to lose integrity of mitochondrial genome, and to be respiration-deficient. Because of the severity of phenotypes associated with the depletion of Pim1, this protease appears to be an essential component of the protein quality control machinery in mitochondria and to exert crucial functions during the biogenesis of this organelle. Nevertheless, its physiological substrates and partners are not fully characterized. Therefore, we used the combination of different proteomic techniques to assess the nature of oxidized protein substrates and physiological partners of Pim1 protease under non-repressing growth conditions. The results presented here supply evidence that Pim1-mediated proteolysis is required for elimination of oxidatively damaged proteins in mitochondria.

Addition of aryl radicals generated from electrochemical reduction of aryl halides on carbon-carbon double bonds.

Abstract Aryl radicals generated by electrochemical reduction of aryl halides in aprotic medium react with styrene and its derivatives to give arylated addition compounds.

Isolation and characterization of an aspartic proteinase gene from cowpea (Vigna unguiculata l. Walp.)

A cowpea (Vigna unguiculata cv. EPACE-1) aspartic proteinase (AP) gene was isolated by genomic Library screening. Sequence analysis shows that this AP gene follows the same pattern of intron/exon number and organization as the other isolated plant AP genes, which are distinct from other solved AP genes. Northern blot analysis revealed that cowpea AP accumulates in leaves and stems but not in roots, indicating tissue-specific expression. An increased accumulation of transcripts during senescence suggests enzyme involvement in this process.

Circadian modulation of proteasome activity and accumulation of oxidized protein in human embryonic kidney HEK 293 cells and primary dermal fibroblasts

The circadian system orchestrates the timing of physiological processes of an organism living in daily environmental changes. Disruption of circadian rhythmicity has been shown to result in increased oxidative stress and accelerated aging. The circadian regulation of antioxidant defenses suggests that other redox homeostasis elements such as oxidized protein degradation by the proteasome, could also be modulated by the circadian clock. Hence, we have investigated whether proteasome activities and oxidized protein levels would exhibit circadian rhythmicity in synchronized cultured mammalian cells and addressed the mechanisms underlying this process. Using synchronized human embryonic kidney HEK 293 cells and primary dermal fibroblasts, we have shown that the levels of carbonylated protein and proteasome activity vary rhythmically following a 24h period. Such a modulation of proteasome activity is explained, at least in part, by the circadian expression of both Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and the proteasome activator PA28αβ. HEK 293 cells showed an increased susceptibility to oxidative stress coincident with the circadian-dependent lower activity of the proteasome. Finally, in contrast to young fibroblasts, no circadian modulation of the proteasome activity and carbonylated protein levels was evidenced in senescent fibroblasts. This paper reports a novel role of the circadian system for regulating proteasome function. In addition, the observation that proteasome activity is modulated by the circadian clock opens new avenues for both the cancer and the aging fields, as exemplified by the rhythmic resistance of immortalized cells to oxidative stress and loss of rhythmicity of proteasome activity in senescent fibroblasts.

The glyoxalase enzymes are differentially localized in epidermis and regulated during ageing and photoageing.

The glyoxalase enzymes are differentially localized in epidermis and regulated during ageing and photoageing Sabrina Radjei, Monique Gareil, Marielle Moreau, Emmanuelle Leblanc, Sylvianne Schnebert, Bertrand Friguet, Carine Nizard and Isabelle Petropoulos Sorbonne Universit es, UPMC Universit e Paris 06, UMR 8256 Biological Adaptation and Ageing IBPS, Paris, France; CNRS UMR 8256, Paris, France; INSERM ERL U1164, Paris, France; LVMH Recherche, Saint-Jean-de-Braye, France Correspondence: Isabelle Petropoulos, Sorbonne Universit es, UPMC, UMR 8256 Biological Adaptation and Ageing IBPS, 4 place Jussieu, 75252 Paris Cedex 05, Paris, France, Tel.: +33144278167, Fax: +33144275140, e-mail: isabelle.petropoulos@upmc.fr

ELECTRON TRANSFER MECHANISMS IN OXIDATIVE SEDIMENT FORMATION IN FUELS. AN ELECTROCHEMICAL INVESTIGATION.

Abstract Electrochemical oxidation of pyrrole and indole gives rise to radical cations and which react with perinaphthenone to give a coupling product similar to that observed in sediments. Under purely chemical conditions, it is shown that with strong acids in absence of oxygen, a ionic mechanism takes place, but that with weaker acids in the presence of oxygen an electron- transfer mechanism may prevail.

ELECTRON TRANSFER MECHANISMS IN OXIDATIVE SEDIMENT FORMATION IN FUELS. II. AN ELECTROCHEMICAL INVESTIGATION OF THE COUPLING BETWEEN PERINAPHTHENE AND INDOLE.

ABSTRACT Cyclic voltammetry and electrolyses in acetonitrile and toluene have indicated the formation of coupling products between perinaphthene and indole similar to those found in the oxidized sediments of fuels. The formation of these coupling products involves intermediates which are one electron oxidized species. This paper discusses the possible mechanisms by which these products are formed.| Photochemical experiments were performed by irradiating the pyrex electrochemical cell with a 300 W tungsten lamp.