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Kinetics of Switchable Proton Escape from a Proton-Wire within Green Fluorescence Noam Agmon*

Summary: Kinetics of Switchable Proton Escape from a Proton-Wire within Green Fluorescence
Noam Agmon*
Department of Physical Chemistry and the Fritz Haber Research Center, The Hebrew UniVersity,
Jerusalem 91904, Israel
ReceiVed: February 19, 2007; In Final Form: April 29, 2007
The emission from the acidic form of the green fluorescence protein (GFP) changes with increasing time and
temperature from t-1/2 to t-3/2 asymptotics. It is shown that a model of proton diffusion along a one-dimensional
hydrogen-bond network within the protein, with a switch (Thr203) allowing for proton escape, explains the
data quantitatively. From a comparison of the model with experiment, we obtain the rate parameters for
proton dissociation from the chromophore (showing an inVerse temperature effect), the ratio of the proton
association constant squared to its diffusion constant (exhibiting no temperature effect), and the time constant
for switch opening (with a significant Arrhenius dependence). Thus, proton dissociation has a small negative
activation energy (assigned to a complex of the anionic chromophore with H3O+
), whereas the switch has a
large positive activation energy (assigned to Thr203 side-chain rotation). Proton migration is possibly the
outcome of the concerted motion of several protons within GFP.
1. Introduction
Protons participate in numerous enzymatic reactions, are
pumped across the cell membrane by bioenergetic proteins


Source: Agmon, Noam - Institute of Chemistry, Hebrew University of Jerusalem


Collections: Chemistry