We investigated the effect of UVB light (290 < or = lambda < or = 320 nm) on the structure and enzymatic activities of Escherichia coli Fpg protein (2,6-diamino-4-hydroxy-5N-methylformamidopyrimidine-DNA glycosylase), a DNA repair enzyme containing a zinc finger motif and five chromophoric Trp residues. Irradiation with UVB light of air-saturated pH 7.4 buffered aqueous solutions of Fpg induces the formation of polymers as shown by sodium dodecyl sulfate polyacrylamide gel electrophoretic analysis. In argon-saturated solutions, polymer formation produces a precipitate. The polymerization quantum yield is 0.07 +/- 0.01 and 0.15 +/- 0.02 in air- and argon-saturated solutions, respectively. In the polymerized Fpg protein, second-derivative absorption spectroscopy indicates that three and one Trp residues are destroyed in air- and argon-saturated solutions, respectively. Polymers are devoid of all three activities of the Fpg protein, whereas the unpolymerized protein retains full activities. Matrix-assisted laser desorption/ionization experiments demonstrate that polymer formation is accompanied by the formation of short polypeptides containing the first 32 or 33 residues of the N-terminal domain. Theses polypeptides are most probably formed by the photolytic cleavage of Fpg protein induced by light absorption by the adjacent Trp-34 residue.

The aim of this work was to study the effect of vacuum sintering conditions and cerium concentration on the optical, luminescent and thermal properties of yttrium-aluminum garnet based ceramics doped with Се3+ cations. Series of ceramic powders were synthesized and samples of luminescent ceramics having the composition Y3-хСехAl5O12 were synthesized where x was in the range 0.01 to 0.025 f.u. We show that the phase composition and grain size distribution of the ceramic powders do not depend on cerium concentration. Without sintering additives, an increase in vacuum sintering temperature from 1675 to 1800 °C leads to an increase in the optical transmittance of luminescent ceramic specimens from 5 to 55% at a 540 nm wavelength and an increase in the thermal conductivity of the samples from 8.4 to 9.5 W/(m ∙ K). It was found that an increase in cerium concentration leads to a shift of the luminescent band peak from 535 to 545 nm where as the width of the luminescent band decreases with an increase in vacuum sintering temperature from 1675 to 1725 °C.

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