Biophysical Journal 59: 4-11 (1991)
© 1991 the Biophysical Society

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Proton transfer dynamics in the nonhomogeneous electric field of a protein.

Laser Laboratory for Fast Reactions in Biology, Department of Biochemistry, Tel Aviv University, Israel.

ABSTRACT

By adsorption of pyranine (8 hydroxypyrene 1, 3, 6 trisulfonate) to lysozyme we create on the positively charged protein a fluorophoric site with a total charge of -3. Photo dissociation of the dye's hydroxyl proton changes its absorption and fluorescence spectrum, permitting a continuous monitoring of the reprotonation dynamics. Absorbance measurements in the microsecond time scale monitor how the bulk protons penetrate the Coulomb cage of the bound dye. Time-resolved fluorescence monitors how the proton is escaping out of the Coulomb cage of the bound dye. These probe reactions were studied with a series of dye-enzyme complexes where the number of free carboxylate was reduced by amidation, increasing the total charge of the complex from +5 to +12.6. The time-resolved measurements demonstrate the complexity of the electric field in the immediate vicinity of the dye. It is consistent with a negative potential wall (of the anion) surrounded by a positive potential wall of proteinaceous moieties.

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