Electron transfer mechanism for regulatory action by nitric oxide

Cell signaling (mechanism and reproductive toxicity): redox chains, radicals, electrons, relays, conduit, electrochemistry, and other medical implications

This article deals with a novel, simple, integrated approach to cell signaling involving basic biochemical principles, and their relationship to reproductive toxicity. Initially, an overview of the biological aspects is presented. According to the hypothetical approach, cell signaling entails interaction of redox chains, involving initiation, propagation, and termination. The messengers are mainly radicals and electrons that are generated during electron transfer (ET) and hydrogen atom abstraction reactions. Termination and initiation processes in the chain occur at relay sites occupied by redox functionalities, including quinones, metal complexes, and imines, as well as redox amino acids. Conduits for the messengers, comprising species with nonbonding electrons, are omnipresent. Details are provided for the various electron transfer processes. In relation to the varying rates of cell communication, rationale is based on electrons and size of radicals. Another fit is similarly seen in inspection of endogenous precursors of reactive oxygen species (ROS); namely, proteins bearing redox moieties, lipid oxidation products, and carbohydrate radicals. A hypothesis is advanced in which electromagnetic fields associated with mobile radicals and electrons play a role. Although radicals have previously been investigated as messengers, the area occupies a minor part of the research, and it has not attracted broad consensus as an important component. For the first time, an integrated framework is presented composed of radicals, electrons, relays, conduits, and electrical fields. The approach is in keeping with the vast majority of experimental observations. Cell signaling also plays an important role in reproductive toxicity. The main classes that cause birth defects, including ROS, radiation, metal compounds, medicinals, abused drugs, and miscellaneous substances, are known to participate in the signaling process. A unifying basis exists, in that both signaling and reproductive toxicity are characterized by the electron transfer-reactive oxygen species-oxidative stress (ET-ROS-OS) scheme. This article also incorporates representative examples of the extensive investigations dealing with various medical implications. There is considerable literature pointing to a role for cell communication in a wide variety of illnesses.

Photochemistry of the [Fe4(μ3-S)3(NO)7]− complex in the presence of S-nucleophiles: A spectroscopic study

Biological systems usually contain cysteine, glutathione or other sulfur-containing biomolecules. These S-nucleophiles were found to affect drastically the [Fe(4)(mu(3)-S)(3)(NO)(7)](-) photolysis pathway generating products completely different from that of the neat cluster, which produces Fe(II) and NO and S(2-). The effect is interpreted in terms of formation of a pseudo-cubane adduct, [Fe(4)(mu(3)-S)(3)(mu(3)-SR)(NO)(7)](2-), whose existence in equilibrium with the parent complex has no detectable influence on the spectral properties, whereas shifts the redox potential and induces photoconversion leading to the Fe(III) species and N(2)O. Characteristic bond lengths, bond angles and atomic Mulliken charges were calculated using semi-empirical quantum chemical methods for the RBS anion and a series of pseudo-cubane complexes with S-donor or N-donor ligands. The results justify the hypothesis of the adduct formation and show that only in case of S-ligands the higher contribution of the Fe(III)-NO(-) components in adduct than in RBS is observed, which on excitation can undergo heterolytic cleavage yielding Fe(III) and NO(-), converted rapidly into N(2)O. These results are crucial in understanding the physiological activity of RBS. Fe(III) formation can be detected only when the S-ligand enables formation of a stable Fe(III) compound; the effect was recorded in the presence of sulfide, thioglycolate, 2-mercaptopropionate, mercaptosuccinate, penicillamine, 2,3-dimercaptosuccinate, 2,3-dimercaptopropanol, and thiocyanate. For all these S-ligands the Fe(III) photoproducts were identified and characterised. In the case of other thiolates, their excess results in fast reduction of Fe(III) to Fe(II), whereas N(2)O can be still detected. Quantum yields of Fe(III) formation in the presence of the S-ligands are considerably higher than that of the Fe(II) photoproduction from neat [Fe(4)(mu(3)-S)(3)(NO)(7)](-).