Effect of albumin on the kinetics of ascorbate oxidation

The fluorescence intensity of the fluorophore in dansyl piperidine-nitroxid e is intramolecularly quenched by the nitroxyl fragment. Therefore, the oxi dation of ascorbic acid by the fluorophore-nitroxide (FN) probe can be moni tored by two independent methods: steady-state fluorescence and electron pa ramagnetic resonance. Bovine serum albumin (BSA) affects the rate of this r eaction. The influence of BSA on the rate is attributed to the adsorption o f both ascorbate and the probe to BSA. Adsorption of ascorbate to BSA is co nfirmed by NMR relaxation experiments. The spatial distribution of the mole cules on the BSA surface changes the availability of ascorbate and FN to ea ch other. The results also point out that, in the presence of BSA, the auto xidation of ascorbate is significantly slowed down. The effect is studied a t different pH values and explained in terms of the electrostatic interacti on between the ascorbate anion and the SSA molecule. (C) 2001 Elsevier Scie nce B.V. All rights reserved.