Abstract
The fluorescence intensity of the fluorophore in dansyl-piperidine nitroxide is intramolecularly quenched by the nitroxyl fragment. Therefore, the oxidation of ascorbic acid by the Fluorophore-Nitroxide (FN) probe can be monitored by two independent methods: EPR and steady-state fluorescence. The adsorption of both ascorbate and FN to BovineSerum Albumin (BSA) influences the rate of this reaction. The spatial distribution of the ascorbate and FN molecules on the BSA surface changes their ability to interact with each other. The effect of BSA on this reaction rate strongly depends on pH and ionic strength since these factors affect the ascorbate binding to the protein. The binding constant of ascorbate to BSA was calculated from kinetic studies. The adsorption of ascorbate to BSA was also confirmed by 1H NMR experiments via measurement of the transverse relaxation time, T2, of ascorbate protons in BSA solutions. Ascorbate binding to BSA resulted in the appearance of a short T2 component in the magnetization decay. The ratio between the short and long components of the magnetization decay reflects the ratio between bound and free ascorbate.
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