Thirty-eighth Annual Meeting March 6-10, 1994 New Orleans Convention Center New Orleans, Louisiana. Wednesday Symposia and Posters, Part IV

<span title="">1994</span> <i title="Elsevier BV"> <a target="_blank" rel="noopener" href="https://fatcat.wiki/container/dez2wau7t5aqvklzwrcsreuwq4" style="color: black;">Biophysical Journal</a> </i> &nbsp;
The amino acid tryptophan is a superb intrinsic probe of peptide and protein structure because its fluorescence is so sensitive to environment. A complex fluorescence decay is usually observed for single tryptophans in polypeptide chains, presumably reporting the heterogeneous microenvironment of the the indole chromophore. The environmental sensitivity derives from two sources: two overlapping electronic transitions with different polarity in the first absorption band and multiple nonradiative
more &raquo; ... decay channels. We have used constrained tryptophan derivatives to dissect the different nonradiative processes of indole. First, the complex fluorescence decays reflect ground-state heterogenity which leads to excited-state heterogeneity. Second, the nonradiative rate of indole includes contributions from several environmentally sensitive pathways: solvent quenching, excited-state proton transfer, and excited-state electron transfer. Solvent quenching refers to the major temperature-dependent nonradiative process that occurs in all indoles in protic solvent. Two types of excited-state proton transfer reactions occur in indoles at neutral pH in the presence of a strong proton donor: intramolecular and intermnolecular. Intraand intermolecular proton transfer rates can be estimated from photochmical reaction yields for H-D exchange at aromatic carbons. Excited-state electron transfer has not been detected directly, but inferred from solute quenching experiments and substituent effects. Preliminary studies suggest that the electron transfer rate is independent of temperature. W-PU-WS3-4 BIOSYNTHETIC INCORPORATION OF TRYPTOPHAN ANALOGS INPROTEINS: EXCITING PROSPECTS FORPROTEiN EmRACTON STUDIES. ((A. G. Szabol.2, C. W. V. Hogue2, and J. Brennan2)) lInstitute fr Biological Scienc National Research Coc Bldg. MS4, Montal Rd., Ota Canada, KIA OR6, 2Dq of Biochemisuty, University ofOtwa, 451 Smyth Rt, Ota Canada, KIH 8MS. Protein-protein intacions e ubiquitus in biochemity and biology and often play a key role in ceilar function. Tne ofthe molecular deai of theae intetiona are importan to the elucidation oftheir role in biological proceaa. NMR a INHIBITORY EFFECT ON GLUTAMATE UPTAKE ((T-I Pengl and S-S Sheu2)) Program in Neurosciencel and Department of Pharmacology2, University of Rochester, Rochester, NY 14642. (Sponsored by V. K. Sharna) Inhibition of glutamate uptake of astrocytes by arachidonic acid (AA) has been implicated to play important roles in glutamate excitotoxicity found in many pathological conditions of the nervous system, such as isehemia, hypoxia and trauma. Transport of glutamate into the cells occurs via a Na+ --glutamate cotransporter which utilizes the Na+ concentration gradient as a driving force for the uptake mechanism. In this report, we studied whether there is a change of intracellular sodium concentration ([Na+]i) induced by AA, and whether this change of [Na+ij accounts for the glutamate uptake inhibition. An astrocyte cell line (RBA-1), which was derived from primary culture of neonatal rat cerebrum, was used in this study. To measure [Na+]i, cells were loaded with the Na+ sensitive fluorescent probe SBFI, and fluorescent signals from single cells were recorded by a photomultiplier tube via fluorescent microscope. Progressive rise of [Na+]i was noted from astrocytes treated with low micromolar concentrations of AA. With 15 jM AA for 10 minutes, [Na+]i increased from 10 mM to 30 mM. This rise of [Na+]i was greatly attenuated by 2 mM Nit, a finding similar to the AA induced change of [Ca+-]j. (Biophys. J. Abstract 61:2,2 p A367 Feb.1992). While 15 jM AA for 10 minutes caused 25% inhibition of glutamate uptake, AA with Niresulted in less than 5% inhibition. These results suggest that AA induced glutamate uptake inhibition in astrocytes is not a direct effect on the transport protein, but is mediated secondarily by an increase of [Na+li which diminishes the driving force needed for glutamate uptake.
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