Browsing by Author "Silva S., E."

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    Exposure of tryptophanyl residues inα-lactalbumin and lysozyme
    (1986) Edwards M., Ana M.; Silva S., E.
    The effect of iodide ion on the tryptophyl fluorescence of the homologous proteins lysozyme and?-lactalbumin in their native form, as well as in their modified structures and in fragments from these proteins was studied. By assessing the contribution to the total fluorescence of the exposed and buried Trp residues, and of the respective fluorescence quantum yields, the quantization of the number of Trp exposed to the solvent for all the species studied was possible. Both native proteins show an important increase in the number of Trp residues exposed to the solvent when treated with denaturing agents. The peptides L-II (aa 13-105) and?-I (aa 1-90) from lysozyme and?-lactalbumin, respectively, showed Trp residues with different degree of exposure, whereas the smaller fragments, L-III (aa 106-129) and?-II (aa 91 123), had all their Trp residues exposed to the solvent.
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    Photochemical reactivity of the homologous proteinsα-lactalbumin and lysozyme
    (1985) Edwards M., Ana M.; Silva S., E.
    The fluorescent behaviour and the photodynamic effect was studied in native and structurally modified lysozyme and?-lactalbumin.The Tyr residues in lysozyme and?-lactalbumin show different sensitivities to the photodynamic effect. The effect is zero in the case of Tyr from native lysozyme. In contrast, the Tyr residues in?-lactalbumin are susceptible to photooxidation, which indicates a greater degree of exposure to the solvent. The three His residues of?-lactalbumin have different degrees of exposure and show two different kinetics of photooxidation whereas the His residue of lysozyme is photooxidized with a single kinetic.Two photooxidation kinetics were obtained for the Trp residues of both native proteins, an indication that in both cases there are Trp residues that are differently exposed to the solvent. The wavelengths of maximum fluorescent emission of the Trp residues were different for the two proteins, an effect which can also be explained in terms of a difference in the environment of these residues. The modified form of these proteins emit at wavelengths longer than those of the native forms. When modified the proteins photooxidize with noticeably greater quantum yields.