Browsing by Author "EDWARDS, AM"

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    EXPOSURE OF TRYPTOPHANYL RESIDUES IN ALPHA-LACTALBUMIN AND LYSOZYME - QUANTITATIVE-DETERMINATION BY FLUORESCENCE QUENCHING STUDIES
    (1986) EDWARDS, AM; SILVA, E
    The effect of iodide ion on the tryptophyl fluorescence of the homologous proteins lysozyme and .alpha.-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 .alpha.-I (aa 1-90) from lysozyme and .alpha.-lactalbumin, respectively, showed Trp residues with different degree of exposure, whereas the smaller fragments, L-III (aa 106-129) and .alpha.-II (aa 91-123), had all their Trp residues exposed to the solvent.
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    OBTENTION OF A PHOTOINDUCED ADDUCT BETWEEN A VITAMIN AND AN ESSENTIAL AMINO-ACID - BINDING OF RIBOFLAVIN TO TRYPTOPHAN
    (1987) SALIMHANNA, M; EDWARDS, AM; SILVA, E
    Studies in animals have suggested that the products of the irradiation of tryptophan in the presence of riboflavin may play a role in the development of hepatic dysfunction during parenteral nutrition. In this paper we describe the formation of an adduct between tryptophan and riboflavin obtained as a consequence of an anaerobic irradiation of these compounds. Through the use of molecular sieves and of an ion-exchange resin it was possible to separate the photo-adduct from the dimer riboflavin and other reaction products. The various fractions were characteized on the basis of their absorption and emission spectra. Also used were measures of anisotropy of fluorescence emission in order to characterize the derived adduct.
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    PHOTOCHEMICAL REACTIVITY OF THE HOMOLOGOUS PROTEINS ALPHA-LACTALBUMIN AND LYSOZYME
    (1985) EDWARDS, AM; SILVA, E
    The fluorescent behavior and the photodynamic effect was studied in native and structurally modified lysozyme and .alpha.-lactalbumin. The Tyr residues in lysozyme and .alpha.-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 .alpha.-lactalbumin are susceptible to photooxidation, which indicates a greater degree of exposure to the solvent. The 3 His residues of .alpha.-lactalbumin have different degrees of exposure and show 2 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 2 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.
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    VISIBLE-LIGHT EFFECTS ON TUMORAL CELLS IN A CULTURE-MEDIUM ENRICHED WITH TRYPTOPHAN AND RIBOFLAVIN
    (1994) EDWARDS, AM; SILVA, E; JOFRE, B; BECKER, MI; DEIOANNES, AE
    When NSO/2 myeloid cell line and teratocarcinoma F9 cells were irradiated in Dulbecco's modified Eagle medium enriched with tryptophan and riboflavin, toxic photoproducts for these tumoral cells were generated. The active participation of O-1(2) and .OH was established using specific scavengers and quenchers. A cytotoxic effect was also observed when unirradiated tumoral cells were incubated in a previously irradiated culture medium enriched with tryptophan and riboflavin. When irradiated medium was used alone, enriched only with tryptophan or only with riboflavin, no toxic effect was observed. The relevance of charge transfer processes between triplet riboflavin and tryptophan in the generation of cytotoxic photoproducts is discussed.