Nature, identification, and properties of intermediates produced byuv excitation of indole derivatives at low and room temperatures. Some applications to tryptophan-containing proteins

Santús, René; Bazin, M.; Aubailly, M.

doi:10.1007/bf03052423

Cited by 70 publications

(4 citation statements)

References 125 publications

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“…Proton transfer to the excited indole, charge (electron) transfer from the indole to an acceptor such as a carbonyl group, photoelectron ejection, intersystem crossing, and internal conversion pathways have been postulated. The extensive literature on the photophysics of indoles including tryptophan derivatives has been reviewed (Santus et al, 1980;Creed, 1984). Saito et al (1984Saito et al ( , 1985 showed that ultraviolet radiation of tryptophan zwitterion in D20 resulted in H-D exchange at C-4 of the indole ring, with a quantum yield of about 0.14, and that the anion did not exchange.…”

Section: Resultsmentioning

confidence: 99%

Fluorescence of tryptophan dipeptides: correlations with the rotamer model

Chen¹,

Knutson²,

Ziffer³

et al. 1991

Biochemistry

132

103

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The multiexponential decay of tryptophan derivatives has previously been explained by the presence of rotamers having different fluorescence lifetimes, but it has been difficult to correlate rotamer structure and physical properties. New time-resolved and static data on dipeptides of the type Trp-X and X-Trp, where X is another aminoacyl residue, are consistent with the rotamer model and allow some correlations. That a dominant rotamer of Trp-X zwitterion has the -NH3+ group near the indole ring was inferred from absorption and fluorescence spectra, titrimetric determination of pKa values, photochemical hydrogen-deuterium-exchange experiments, decay-associated spectra, quantum yields, and decay kinetics. Analysis of the lifetime and quantum yield data for Trp dipeptides, especially X-Trp, suggests that static self-quenching is not uncommon. Highly quenched and weak components of the fluorescence do not contribute to the calculated mean lifetime, thus resulting in apparent static quenching. We propose the term quasi-static self-quenching (QSSQ) to distinguish this phenomenon from quenching due to ground-state formation of a dark complex. Mechanisms of quenching and the structure of statically quenched rotamers are discussed. The occurrence of QSSQ supports the idea that rotamers interconvert slowly. A major perceived deficiency of the rotamer model, namely, the apparent inability to predict reasonable rotamer populations from fluorescence decay data, may result from the presence of statically quenched species, which do not contribute to the fluorescence.

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Section: Resultsmentioning

confidence: 99%

Fluorescence of tryptophan dipeptides: correlations with the rotamer model

Chen¹,

Knutson²,

Ziffer³

et al. 1991

Biochemistry

132

103

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show abstract

“…1 . atom may be produced via two alternative photohomolytic cleavages on a catecholic indole; (1) 0-H bond fission, or N-H bond fission (Land et al, 1986;Santus et al, 1980). Preliminary laser flash photolysis results indicate the presence of both the indolesemiquinone and a transient which has been assigned as a nitrogen-centered radical (personal communication-E. J.…”

Section: Melanogenic Metabolite Photochemistrymentioning

confidence: 99%

PHOTOCHEMISTRY and PHOTOBIOLOGY OF MELANOGENIC METABOLITES: FORMATION OF FREE RADICALS*

Koch

Chedekel

1987

Photochem & Photobiology

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Normal melanocytes produce specialized subcellular organelles called melanosomes within which the biochemical processes of melanogenesis occurs. During sunlight‐induced melanogenesis, the melanocyte‐specific enzyme tyrosinase catalyzes the oxidative polymerization of 3,4‐dihydroxyphenyl‐alanine (DOPA) to melanin. Nucleophilic addition of cysteine to tyrosinase‐generated dopaquinone leads to the formation of cysteinyldopas, precursors of pheomelanin and excreted by‐products of eumelanogenesis. Under conditions of low sulfhydryl content, dopaquinone undergoes a 1,4 intramolecular cycloaddition to yield, after further oxidation, 5,6‐dihydroxyindoles and/or 5,6‐dihydroxy‐2‐carboxyindoles. These indolic melanogenic intermediates and their O‐methylated metabolites, like cysteinyldopas, are excreted by actively pigmenting as well as dormant melanocytes. Indeed, it has been determined that in humans, the serum and urine concentrations of these melanogenic metabolites increase dramatically following exposure to sunlight, UVA (315‐400 nm), UVB (290‐315 nm) exposure, as well as during PUVA therapy and in melanoma patients, and thus have proved to be excellent biochemical markers of normal and pathological melanocyte function. While controlled light exposure or PUVA therapy generally lead to 100‐300% increases in 5‐S‐cysteinyldopa (5SCD) and 5‐methoxy‐6‐hydroxyindole‐2‐carboxylic acid (6HMICA) serum levels (normal concentration about 4–16 nmol l‐1), the local concentrations in the skin and especially in the actively pigmenting melanocyte may be as high as 200 μM. Evidence is presented to document that a number of catecholic melanin precursors, including cysteinyldopas and dihydroxyindoles, are photochemically unstable in the presence of biologically relevant ultraviolet radiation (i.e. wavelengths ± 300 nm). Initial photochemical processes involve free radical production; continued photolysis yields polymeric photoproducts. Radicals produced during melanogenic metabolite photolysis have been identified by ESR spin trapping, laser flash photolysis and pulse radiolysis techniques and include hydrated electrons (eaq), hydrogen atoms (H'), hydroxyl radicals (OH), semiquinones, aryl thiyl (ArS), and alanyl carbon‐based radicals. In vitro investigations of the potential photobiological significance of these reactions have demonstrated photolysis of cysteinyldopas may lead to photoinitiated DNA binding and single strand break induction. The above mentioned radical species may also damage proteins and initiate lipid peroxidation. Definitive evidence for the occurrence of these phototoxic reactions in vivo is currently unavailable, however our in vitro studies suggest a possible role for melanogenic metabolite photolysis in acute and chronic solar responses of human skin.

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“…1 /~~ = k5 + k6 + k l ( k Z + k3)/k4 (2) where ki are phenomenological rate constants and aISc is [Cretam5Br]Br2 was obtained by the same method as [Crmearn5Br]Brzl5 by using ethylamine instead of methylamine. tr~ns-[Cr(N-N)~Br~]Br complexes (N-N = en, pn, tn) were prepared by treating ca.…”

Section: Intraductionmentioning

confidence: 99%

The role of hydrogen vibrations in the radiationless deactivation of chromium(III)-alkylamine complexes in their lowest doublet state

Kuehn¹,

Wasgestian²,

Kupka³

1981

J. Phys. Chem.

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A series of chromium(II1)-alkylamine complexes with CrNe skeletons have been synthesized. These complexes have similar electronic properties but different numbers of N-H bonds, ranging from 8 to 18. Measurements of absorption spectra, relative phosphorescence quantum yields, and phosphorescence decay times, obtained at liquid nitrogen temperature, showed that there is a good correlation between the radiationless transition rate and the number of active hydrogen atoms attached to the donor atoms. For the dependence of the electronic relaxation rate on the number of the maximum frequency N-H vibrations a theoretical expression is derived, which includes both the effects of configurational changes and of frequency changes in the first coordination layer. This expression adequately predicts the dependence of the nonradiative rate from the vibrational degeneracy and the displacement of the maximum frequency modes.

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Nature, identification, and properties of intermediates produced byuv excitation of indole derivatives at low and room temperatures. Some applications to tryptophan-containing proteins

Cited by 70 publications

References 125 publications

Fluorescence of tryptophan dipeptides: correlations with the rotamer model

Fluorescence of tryptophan dipeptides: correlations with the rotamer model

PHOTOCHEMISTRY and PHOTOBIOLOGY OF MELANOGENIC METABOLITES: FORMATION OF FREE RADICALS*

The role of hydrogen vibrations in the radiationless deactivation of chromium(III)-alkylamine complexes in their lowest doublet state

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