Synthesis and antimalarial activity of 2-methoxyprop-2-yl peroxides derivatives

2-Methoxyprop-2-yl peroxides were synthesized and evaluated in vitro against Plasmodium falciparum. These acyclic artemisinin-related peroxides revealed moderate to good activity but were devoid of alkylating property towards the synthetic model of heme Mn(II)-TPP.     

Alkylation of manganese(II) tetraphenylporphyrin by antimalarial fluorinated artemisinin derivatives

The alkylating properties of two artemisinin derivatives bearing a trifluoromethyl substituent at C10 were evaluated toward manganese(II) tetraphenylporphyrin, considered as a heme model. Chlorin-type covalent adducts were obtained by alkylation of the porphyrin ring by C-centered radicals derived from reductive activation of the peroxide function of the drugs.     

Changes in the physiological and agricultural characteristics of peat-based Bradyrhizobium japonicum inoculants after long-term storage

Commercial soybean inoculants processed with sterilised peat and stored at 20 °C for 1–8 years were used as experimental materials to assess the changes in the physiological activity of Bradyrhizobium japonicum after storage. Viable counts decreased and physiological characteristics of the bacterium changed during storage, with an increase in the time taken for colony appearance on a medium without yeast extract, an increase in the lag time for nodule appearance on soybean grown in glass tubes and a decrease in survival on seeds. All the inoculants produced a significant increase in grain yield in a field experiment. The percentage of efficient cells in the field (relative to the plate counts) decreased as the length of storage increased. These results suggest that the physiological activity of B. japonicum cells changes after storage. Practical implications for inoculant quality control are discussed. Received: 20 September 1999 / Received revision: 3 March 2000 / Accepted: 6 March 2000     

Mapping the fMet-tRNA(f)(Met) binding site of initiation factor IF2

The interaction between fMet-tRNA(f)(Met) and Bacillus stearothermophilus translation initiation factor IF2 has been characterized. We demonstrate that essentially all thermodynamic determinants governing the stability and the specificity of this interaction are localized within the acceptor hexanucleotide fMet-3'ACCAAC of the initiator tRNA and a fairly small area at the surface of the beta-barrel structure of the 90-amino acid C-terminal domain of IF2 (IF2 C-2). A weak but specific interaction between IF2 C-2 and formyl-methionyl was also demonstrated. The surface of IF2 C-2 interacting with fMet-tRNA(f)(Met) has been mapped using two independent approaches, site- directed mutagenesis and NMR spectroscopy, which yielded consistent results. The binding site comprises C668 and G715 located in a groove accommodating the methionyl side-chain, R700, in the vicinity of the formyl group, Y701 and K702 close to the acyl bond between fMet and tRNA(f)(Met), and the surface lined with residues K702-S660, along which the acceptor arm of the initiator tRNA spans in the direction 3' to 5'.     

Oxidative damage generated by an oxo-metalloporphyrin onto the human telomeric sequence

The cationic metalloporphyrin Mn-TMPyP activated by KHSO(5) has been used as cleaver of an oligonucleotide containing the four human telomere repeats of 5'-GGGTTA. This oligonucleotide formed an intramolecular quadruplex DNA under 200 mM KCl as probed by DMS footprinting and could fold into different quadruplex structures under 200 mM NaCl. We found that the oxo-metalloporphyrin was able to mediate efficient oxidative cleavage of the quadruplex. The location of damage showed that the metalloporphyrin was able to bind to the last G-tetrad of the quadruplex structure via an external interaction. This metalloporphyrin-G-tetrad interaction needs a relatively high flexibility of the single-stranded linker regions to allow the partial stacking of the metalloporphyrin with the last G-tetrad planar structure. The oxidative damage consisted of guanine oxidation within the interacting G-tetrad together with an 1'-carbon hydroxylation of deoxyribose residues of the thymidine residues located on the neighboring single-stranded loop. So the high-valent oxo-metalloporphyrin is able to mediate both electron-abstraction or H-abstraction on G or T residues, respectively, within the DNA quadruplex target.     

Mechanisms of DNA cleavage by copper complexes of 3-clip-phen and of its conjugate with a distamycin analogue

Mechanisms of DNA oxidation by copper complexes of 3-Clip-Phen and its conjugate with a distamycin analogue, in the presence of a reductant and air, were studied. Characterisation of the production of 5-methylenefuranone (5-MF) and furfural, associated with the release of nucleobases, indicated that these copper complexes oxidised the C1′ and C5′ positions of 2-deoxyribose, respectively, which are accessible from the DNA minor groove. Oxidation at C1′ was the major degradation route. Digestion of DNA oxidation products by P1 nuclease and bacterial alkaline phosphatase allowed characterisation of glycolic acid residues, indicating that these copper complexes also induced C4′ oxidation. However, this pathway was not associated with base propenal release. The ability of the copper complex of the 3-Clip-Phen conjugate with the distamycin analogue to produce sequence-selective DNA cleavage allowed confirmation of these mechanisms of DNA oxidation by PAGE. Comparison of DNA cleavage activity showed that conjugation of 3-Clip-Phen with a DNA minor groove binder, like the distamycin analogue, decreased both its ability to perform C1′ oxidation as well as the initial rate of the reaction, but this conjugate is still active after 5 h at 37°C, making it an efficient DNA cleaver.     

Reduction of Presynaptic Action Potentials by PAD: Model and Experimental Study

A compartmental model of myelinated nerve fiber was used to show that primary afferent depolarization (PAD), as elicited by axo-axonic synapses, reduces the amplitude of propagating action potentials primarily by interfering with ionic current responsible for the spike regeneration. This reduction adds to the effect of the synaptic shunt, increases with the PAD amplitude, and occurs at significant distances from the synaptic zone. PAD transiently enhances the sodium current activation, which partly accounts for the PAD-induced fiber hyperexcitability, and enhances sodium inactivation on a slower time course, thus reducing the amplitude of action potentials. In vivo, intra-axonal recordings from the intraspinal portion of group I afferent fibers were carried out to verify that depolarizations reduced the amplitude of propagating action potentials as predicted by the model. This article suggests PAD might play a major role in presynaptic inhibition.     

Protonmotive Mechanism of Heme-Copper Oxidases

The mechanism of coupling of proton and electron transfer in oxidases is reviewed and related to the structural information that is now available. A glutamate trap mechanism for proton/electron coupling is described.     

Reaction of wild-type and Glu243Asp variant yeast cytochrome c oxidase with O2

We have studied internal electron transfer during the reaction of Saccharomyces cerevisiae mitochondrial cytochrome c oxidase with dioxygen. Similar absorbance changes were observed with this yeast oxidase as with the previously studied Rhodobacter sphaeroides and bovine mitochondrial oxidases, which suggests that the reaction proceeds along the same trajectory. However, notable differences were observed in rates and electron-transfer equilibrium constants of specific reaction steps, for example the ferryl (F) to oxidized (O) reaction was faster with the yeast (0.4 ms) than with the bovine oxidase (~ 1 ms) and a larger fraction Cu_A was oxidized with the yeast than with the bovine oxidase in the peroxy (P_R) to F reaction. Furthermore, upon replacement of Glu243, located at the end of the so-called D proton pathway, by Asp the P_R → F and F → O reactions were slowed by factors of ~ 3 and ~ 10, respectively, and electron transfer from Cu_A to heme a during the P_R → F reaction was not observed. These data indicate that during reduction of dioxygen protons are transferred through the D pathway, via Glu243, to the catalytic site in the yeast mitochondrial oxidase. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.