In vivo EPR measurement of glutathione in tumor-bearing mice using improved disulfide biradical probe.

Disulfide nitroxide biradicals, DNB, have been used for glutathione, GSH, measurements by X-band electron paramagnetic resonance, EPR, in various cells and tissues. In the present paper, the postulated potential use of DNB for EPR detection of GSH in vivo was explored. Isotopic substitution in the structure of the DNB was performed for the enhancement of its EPR spectral properties.

Mapping local protein electrostatics by EPR of pH-sensitive thiol-specific nitroxide.

A first thiol-specific pH-sensitive nitroxide spin-label of the imidazolidine series, methanethiosulfonic acid S-(1-oxyl-2,2,3,5,5-pentamethylimidazolidin-4-ylmethyl) ester (IMTSL), has been synthesized and characterized. X-Band (9 GHz) and W-band (94 GHz) EPR spectral parameters of the new spin-label in its free form and covalently attached to an amino acid cysteine and a tripeptide glutathione were studied as a function of pH and solvent polarity. The pKa value of the protonatable tertiary amino group of the spin-label was found to be unaffected by other ionizable groups present in side chains of unstructured small peptides.

Mechanistic studies of the reactions of nitrone spin trap PBN with glutathiyl radical.

We performed mechanistic studies of the reaction of PBN with the physiologically relevant glutathiyl radical, GS*, formed upon oxidation of the intracellular antioxidant, glutathione, GSH. The scavenging rate constant of GS* by PBN has been measured directly by laser flash photolysis and indirectly by competitive EPR of the spin adduct of PBN and another spin trap, DMPO (5,5-dimethyl-1-pyrroline N-oxide), and was found to be 6.7 x 107 M(-1) s(-1).

Difficulties in building radiation-generated three-spin systems using spin-labeled luminophores.

Aromatic compounds are well-known acceptors of primary radical ions that are formed under high-energy irradiation of nonpolar systems. Thus formed radical ion pairs recombine and produce magnetosensitive fluorescence, which helps study the short-lived radical ions. It was initially suggested that a simple introduction of a spin label into the original arene would allow an easy transition from two-spin to three-spin systems, retaining the experimental techniques available for radical pairs.

Quantitative determination of SH groups using 19F NMR spectroscopy and disulfide of 2,3,5,6-tetrafluoro-4-mercaptobenzoic acid.

A new method of measurement of thiol concentration by 19F NMR spectroscopy is developed. The method is based on the detection of products of the exchange reaction of thiols with a newly synthesized fluorinated disulfide, 2,3,5,6-tetrafluoro-4-mercaptobenzoic acid (BSSB). A significant broadening of the 19F NMR signal of BSSB in the presence of thiols was observed and attributed to the exchange reaction between the parent disulfide and 2,3,5,6-tetrafluoro-4-mercaptobenzoic acid.

19F NMR measurements of NO production in hypertensive ISIAH and OXYS rats.

Recently we demonstrated the principal possibility of application of 19F NMR spin-trapping technique for in vivo *NO detection [Free Radic. Biol. Med.

Site-directed electrostatic measurements with a thiol-specific ph-sensitive nitroxide: differentiating local pK and polarity effects by high-field EPR.

This communication describes the use of a methanethiosulfonate derivative of an imidazolidine nitroxide, methanethiosulfonic acid S-(1-oxyl-2,2,3,5,5-pentamethyl-imidazolidin-4-ylmethyl) ester, IMTSL, for site-directed pKa determination of peptides by electron paramagnetic resonance. This spin label is covalently attached to the thiol group of unique cysteines incorporated into peptide structures. The tertiary amine nitrogen N3 of the label readily participates in proton exchange reactions, which are monitored through changes in EPR spectra of nitroxide moiety.

Redox-sensitive mechanism of no scavenging by nitronyl nitroxides.

Nitronyl nitroxides, NN., have been increasingly used in the field of NO-related studies as specific antagonists of NO. .

Nonradical mechanism of (bi)sulfite reaction with DEPMPO: cautionary note for SO3*- radical spin trapping.

Knowledge of the formation of radicals from sulfites, in vivo, is of interest in understanding the allergic and inflammatory responses to environmental sulfur dioxide exposure. Sulfite anion trioxide (SO(3)(-*)) radical formation was measured in mice, preloaded with the spin trap, 5-(diethoxy-phosphoryl)-5-methyl-pyrrolidine-N-oxide, (DEPMPO). Based on spin trapping NMR, a surprising quantity of reduced SO(3)(-*)-adduct was observed that did not depend on co-administration of oxidizing agents, suggesting a possible nonradical reaction between (bi)sulfite and DEPMPO.