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Biomedical subjects

R Santus

Publications and source records attributed to R Santus.

At least 145 records · Page 8Linked to original sources
PubMed1984

Binding of 5-methoxypsoralen to human serum low density lipoproteins.

5-methoxypsoralen (5-MOP) binds to human serum low density lipoproteins (LDL) according to a two-step process. Scatchard analysis of the first step yields K = 1.4 X 10(5) M-1 and 4 binding sites. It involves the LDL apoprotein. The second step corresponds to a solubilization, in the lipidic core, of congruent to 45 molecules of 5MOP per LDL molecule. It is accompanied by a large blue shift of the 5MOP fluorescence. The ability of LDL to bind 5MOP and to carry it into various cells may explain some biological effects sometimes encountered during PUVA therapy.

5-Methoxypsoralen↗
PubMed1984

Influence of DNA binding on the formation and reactions of tryptophan and tyrosine radicals in peptides and proteins.

The rate constant of the one-electron oxidation of the tryptophan (Trp) or tyrosine (Tyr) residues by Br- X 2 radical anions is strongly decreased when the peptides are bound to DNA. Oxidation by N X 3 is much less affected by binding. These results can be explained by electrostatic repulsion between the charged polyphosphate backbone and the Br- X 2 radicals. Once oxidized, the interacting aromatic residues react with the DNA in a first order process with a rate constant of the order 10(3) s-1. These results have been extended to the single strand binding protein: the product of gene 32 of phage T4 (gp 32). The pulse radiolysis study suggests that one Trp residue of the protein oxidized by the Br- X 2 radicals reacts with the DNA in the complex while one Tyr residue is buried upon association. It is also shown that the exposure of Trp and Tyr residues to radical attack depends on whether the T4 SSB protein is bound to native or heat-denatured DNA.

DNA↗
PubMed1983

Physicochemical properties and stability of anthralin in model systems and human skin.

The physico-chemical properties and the stability of anthralin, a potent antipsoriatic agent, has been investigated in model systems by optical absorption and fluorescence spectroscopy and by gas chromatography coupled to mass spectrometry. Systematic studies were carried out on anthralin and its oxidation products (1,8-dihydroxyanthraquinone and 1,8-1',8'-tetrahydroxydianthron). Anthralin and 1,8-dihydroxyanthraquinone are shown to readily bind to human serum albumin and not to DNA. Anthralin bound to albumin readily oxidizes, yielding the 1,8-dihydroxyanthraquinone which is fairly stable. These results are correlated with those obtained with intact whole human epidermis and suction blister fluid showing that, in the former case, anthralin binds to protein as suggested by absorption and fluorescence spectroscopies. Gas chromatography-mass spectrometry analysis makes it easy to detect anthralin and 1,8-dihydroxyanthraquinone in suction blister fluid doped with anthralin but not in suction blister obtained after topical application on normal human skin.

Anthracenes↗
PubMed1982

Pulse radiolysis and cellular studies of a new class of radiosensitizers: 2-nitrobenzofurans.

A group of 2-nitrobenzofurans possessing antibacterial and antiparasitic properties have now been shown to be potential radiosensitizers from investigations in simple aqueous solution by pulse radiolysis and from survival studies in yeast. The radical anions of several 2-nitrobenzofurans were formed by the rapid reaction of the parent molecules with hydrated electrons or with various pyrimidine electron adducts. Studies of equilibria between these radical anions, the parent nitrobenzofurans and the corresponding species derived from quinones with known one-electron reduction potentials, showed that the one-electron reduction potentials of all the furans under investigation lie between -285 and -309 mV. They are thus more electron affinic than the nitroimidazoles (misonidazole and metronidazole) currently under clinical evaluation. 5-Hydroxy- and 7-hydroxy-2-nitrobenzofuran were demonstrated to form weak complexes with DNA (binding constant 80 M-1) and strong complexes with HSA (binding constant 10(5)M-1). In the yeast Saccharomyces cerevisiae the nitrobenzofurans exert radiosensitizing effects on survival either similar to or higher than misonidazole.

Benzofurans↗
PubMed1982

One-electron photoreduction of bacterial cytochrome P-450 by ultraviolet light. I. Steady-state irradiations.

Bacterial ferric cytochrome P-450 can be photoreduced by ultraviolet light in presence of camphor as shown by the formation of the ferrous cytochrome P-450--CO complex absorbing at 446 nm in CO-saturated solutions. This photoreduction can only be performed with wavelengths (lambda less than 315 nm) corresponding to the absorption of light by aromatic residues and in particular, tryptophan. The primary process leading to the photoreduction is thus the photoionization of tryptophan residue(s) near the active site of the protein as deduced from competitive electron scavenging with N2O. In agreement with results obtained with chemical reduction, the quantum yield of photoreduction is proportional to the content of the high-spin state of the ferric cytochrome P-450 solution. It is also shown that the camphor concentration affects the CO binding.

Camphor↗
PubMed1982

One-electron photoreduction of bacterial cytochrome P-450 by ultraviolet light. II. A study using laser flash photolysis of the dynamics of the reduction of bacterial cytochrome P-450 in the presence of carbon monoxide. The role of the protein conformation.

The intramolecular photoreduction of the bacterial cytochrome P-450 demonstrated by the formation of the complex of reduced cytochrome m with camphor and CO has been studied by photolysis with a laser flash at 265 nm. This photoreduction of the heme follows the photoionization of a proximal aromatic amino acid residue and especially tryptophan in the nanosecond time scale as evidenced by the N2O effect on the reduction yield. However most of the hydrated electrons released in the solution do not react with the ferric porphyrin. In agreement with steady state studies, the quantum yield for formation of the complex of reduced cytochrome m with camphor and CO is proportional to the concentration of the high-spin species. The low-spin ferric porphyrin is thus not reducible by photoejected electrons. It is also shown that the growth kinetics of the transient absorbance at 446 nm characterizing the complex of reduced cytochrome m with camphor and CO correspond to a structural change affecting the protein and not to the formation of the complex of CO with the camphor-bound reduced cytochrome in which occurs on a shorter time scale in the present experimental conditions.

Carbon Monoxide↗
PubMed1977

A pulse-radiolysis study of the reaction of hydrated electrons with N'-formylkynurenine and related compounds: electron-transfer reactions with nucleic acid components.

The reactivity of N'-formylkynurenine (FK) derivatives towards eaq has been investigated. The reduced transient species have been characterized (lambda max approximately 340, 440 nm, epsilon lambda max approximately 3000-1000 M-1 cm-1, pKa approximately 7.8). Owing to the strong FK electron affinity, electron-transfer reactions occur from purine (except guanine) and pyrimidine electron adducts to FK (k approximately 2-7 x 10(9) M-1 s-1). As some FK derivatives bind to DNA (or polynucleotides) the protective effect of complexation on FK-DNA (or polynucleotides) adduct formation has been investigated.

DNA↗