ascorbic-acid and sodium-sulfide

The DNA of patients taking the immunosuppressant and anticancer drugs azathioprine or 6-mercaptopurine contains 6-thioguanine (6-TG). The skin of these patients is selectively sensitive to ultraviolet A radiation (UVA) and they suffer an extremely high incidence of sunlight-induced skin cancer with long-term treatment. DNA 6-TG interacts with UVA to generate reactive oxygen species, which oxidize 6-TG to guanine sulphonate (G(SO3)). We suggested that G(SO3) is formed via the reactive electrophilic intermediates, guanine sulphenate (G(SO)) and guanine sulphinate (G(SO2)). Here, G(SO2) is identified as a significant and stable UVA photoproduct of free 6-TG, its 2'-deoxyribonucleoside, and DNA 6-TG. Mild chemical oxidation converts 6-TG into G(SO2), which can be further oxidized to G(SO3)-a stable product that resists further reaction. In contrast, G(SO2) is converted back to 6-TG under mild conditions. This suggests that cellular antioxidant defences might counteract the UVA-mediated photooxidation of DNA 6-TG at this intermediate step and ameliorate its biological effects. In agreement with this possibility, the antioxidant ascorbate protected DNA 6-TG against UVA oxidation and prevented the formation of G(SO3).

Topics: Arylsulfonates; Ascorbic Acid; DNA; Guanine; Oxidation-Reduction; Photochemical Processes; Sulfides; Thioguanine; Ultraviolet Rays

Hydrogen sulfide (H(2)S), a gasotransmitter, induces neuronal differentiation characterized by neuritogenesis and functional up-regulation of high voltage-activated Ca(2+) channels, via activation of T-type Ca(2+) channels in NG108-15 cells. We thus analyzed signaling mechanisms for the H(2)S-evoked neuronal differentiation. NaHS, a donor for H(2)S, facilitated T-type Ca(2+) channel-dependent membrane currents, an effect blocked by ascorbic acid that selectively inhibits Ca(v)3.2 among three T-type channel isoforms. NaHS, applied once at a high concentration (13.5 mM) or repetitively at a relatively low concentration (1.5 mM), as well as ionomycin, a Ca(2+) ionophore, evoked neuritogenesis. The neuritogenesis induced by NaHS, but not by ionomycin, was abolished by mibefradil, a T-type Ca(2+) channel blocker. PP2, a Src kinase inhibitor, completely suppressed the neuritogenesis caused by NaHS or ionomycin, while it only partially blocked neuritogenesis caused by dibutyryl cAMP, a differentiation inducer. NaHS, but not dibutyryl cAMP, actually caused phosphorylation of Src, an effect blocked by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl, an intracellular Ca(2+) chelator, mibefradil or ascorbic acid. The up-regulation of high voltage-activated currents in the cells treated with NaHS was also inhibited by PP2. Together, our data reveal that Src kinase participates in the T-type Ca(2+) channel-dependent neuronal differentiation caused by NaHS/H(2)S in NG108-15 cells.

Topics: Animals; Ascorbic Acid; Calcium Channel Blockers; Calcium Channels, T-Type; Cell Differentiation; Cell Line, Tumor; Hybrid Cells; Hydrogen Sulfide; Ion Channel Gating; Ionomycin; Ionophores; Mibefradil; Mice; Neurites; Neurons; Patch-Clamp Techniques; Phosphorylation; Rats; src-Family Kinases; Sulfides

Experimental evidence has shown that a beverage containing Sunset Yellow FCF (labelled as E110 in the European Union), when exposed to natural conditions of summer temperature and sunlight, losses its colour. To possibly identify the degradation pathway and collect information on the potential toxicity of the uncoloured species formed, different degradation conditions, under both oxidising and reducing environments, were simulated in laboratory. Experiments were carried out under the following conditions: (i) thermally induced degradation, (ii) visible photo induced degradation, (iii) UV-photo induced conditions in oxidising environment (addition of hydrogen peroxide, Fenton reaction) and (iv) UV-photo induced conditions in reducing environment (addition of sulphide and ascorbic acid, addition of ascorbic acid in the absence and in the presence of saccharose). Decolourisation process was observed in oxidant conditions when applying the Fenton reaction but the reaction was too quick to be progressively followed. On the other hand, it was also possible to study the degradation reaction observed in reducing conditions in the presence of ascorbic acid. The HPLC-MS results gave evidence for the cleavage of the double bond and the protonation of the azo groups. The loss of colour is therefore not due to a mineralization process but to the formation of a dimeric form of 5-amino-6-hydroxy-2-naphthalene sulfonate and, likely, of p-amino-benzensulfonate.

Topics: Ascorbic Acid; Azo Compounds; Beverages; Chromatography, High Pressure Liquid; Color; Food Coloring Agents; Nitrogen; Oxidation-Reduction; Spectrometry, Mass, Electrospray Ionization; Sulfides; Sunlight; Ultraviolet Rays

A completely defined growth medium has been developed to determine the nitrogen requirements for several species of ruminal bacteria, and has revealed two strains which are impaired in de novo biosynthesis of certain amino acids. Using NH4Cl as a sole nitrogen source, the medium supported growth of Butyrivibrio, Selenomonas, Prevotella and Streptococcus species. One strain of B. fibrisolvens (E14) and one strain of P. ruminicola (GA33) did not grow in the presence of NH4Cl until the medium was supplemented with amino acids or peptides. For B. fibrisolvens strain E14, methionine was identified as the specific growth-limiting amino acid although methionine alone did not support growth in the absence of NH4Cl. For P. ruminicola strain GA33, any individual amino acid other than methionine or cysteine could supplement the medium and support growth. Enzyme assays confirmed a lack of NADH and NADPH-dependent glutamate dehydrogenase (GDH) activities in this strain.

Topics: Amino Acids; Animals; Ascorbic Acid; Bacteria, Anaerobic; Culture Media; Nitrogen; Rumen; Sulfides

Holo and apo adrenodoxin were studied by differential scanning calorimetry, absorption spectroscopy, limited proteolysis, and size-exclusion chromatography. To determine the conformational stability of adrenodoxin, a method was found that prevents the irreversible destruction of the iron-sulfur center. The approach makes use of a buffer solution that contains sodium sulfide and mercaptoethanol. The thermal transition of adrenodoxin takes place at Ttrs = 46-57 degrees C, depending on the Na2S concentration with a denaturation enthalpy of delta H = 300-380 kJ/mol. From delta H versus Ttrs a heat capacity change was determined as delta Cp = 7.5 +/- 1.2 kJ/mol/K. The apo protein is less stable than the holo protein as judged by the lower denaturation enthalpy (delta H = 93 +/- 14 kJ/mol at Ttrs = 37.4 +/- 3.3 degrees C) and the higher proteolytic susceptibility. The importance of the iron-sulfur cluster for the conformational stability of adrenodoxin and some conditions for refolding of the thermally denatured protein are discussed.

Topics: Adrenodoxin; Animals; Apoproteins; Ascorbic Acid; Calorimetry, Differential Scanning; Cattle; Chymotrypsin; Electrophoresis, Polyacrylamide Gel; Hydrogen-Ion Concentration; Mercaptoethanol; Protein Conformation; Protein Denaturation; Protein Folding; Spectrophotometry; Sulfides; Temperature; Thermodynamics; Urea

Topics: Anaerobiosis; Ascorbic Acid; Bacteria, Anaerobic; Clostridium; Cysteine; Electron Transport; Ferredoxins; Oxidation-Reduction; Paraquat; Sulfides; Thioglycolates