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[en] UV light has often been used to induce the formation of covalent bonds between DNA (or RNA) and tightly-bound protein molecules. However, the internal photoreactions of nucleic acids and proteins limit the yield and complicate the analysis of intermolecular crosslinks. In an ongoing search for improved reaction specificity or new photoreactions in these systems, we have employed UV photons from a Nd:YAG-pumped dye laser and mid-IR photons from the Vanderbilt FEL. Having crosslinked several protein-nucleic acid systems with nanosecond UV laser pulses, we are currently studying the effect of various IR wavelengths on a model system (gene 32 protein and poly[dT]). We have found that irradiation with sufficiently intense FEL macropulses creates an altered form of gene 32 protein which was not observed with UV-only irradiation. The electrophoretic nobility of the product is consistent with the formation of a specific protein-protein crosslink. No evidence of the non-specific protein damage typically induced by UV light is found. The yield of the new photoproduct is apparently enhanced by exposure to FEL macropulses which are synchronized with UV laser pulses. With ideal exposure parameters, the two-color reaction effectively competes with UV-only reactions. Experiments designed to determine the reaction mechanism and to demonstrate FEL-induced reactions in other protein-nucleic acid systems are currently underway

[en] Experimental evidence is presented for FEL induced photothermal protein chemistry and FEL modulation of microtubule dynamics. These findings are discussed in terms of previous investigations of FEL tissue ablation to explore the importance of the micropulse structure of the Mark-III FEL. We propose various roles for localized heating in FEL modulation of the dynamics of biological macromolecules. Potential medical applications are described. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)

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[en] The aim of the study was to present the brain metabolic changes in HIV-positive patients at different stages of the disease using HMRS. MRI and HMRS were performed in 19 patients (4 women, 15 men), 23 to 49 years old, using 1.5 T Signa Horizon (GEMS) MR system. In 4 patients AIDS dementia complex was clinically confirmed (group 1), while the remaining patients had no clinical changes relating to CNS (group 2). MRI. In the group 1, brain atrophy and focal hyperintense lesion in T2-weighted MR images, hypointense lesion in T1-weighted MR images in the centrum semiovale and in the periventricular white matter, were dominant. In the group 2, in 10 cases no CNS changes were observed and in 5 remaining cases moderate degree of brain atrophy was noticed. HMRS: In the group 1, a significant decrease of NAA/Cr, an increase of Cho/Cr, mI/Cr and Lac/Cr ratios were observed. In the group 2, an insignificant decrease of NAA/Cr ratios, a moderate increase in Cho/Cr, and a significant increase mI/Cr ratios were observed. HMRS is a method that broadens CNS diagnostic potential in HIV-positive patients. It enables us to determine the phase of the process involved and image metabolite changes in cases without morphological manifestation. (author)

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