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Sensing pH via p-cyanophenylalanine fluorescence: Application to determine peptide pKa and membrane penetration kinetics.

Analytical biochemistry (2015-05-04)
Ileana M Pazos, Ismail A Ahmed, Mariana I León Berríos, Feng Gai
ABSTRACT

We expand the spectroscopic utility of a well-known infrared and fluorescence probe, p-cyanophenylalanine, by showing that it can also serve as a pH sensor. This new application is based on the notion that the fluorescence quantum yield of this unnatural amino acid, when placed at or near the N-terminal end of a polypeptide, depends on the protonation status of the N-terminal amino group of the peptide. Using this pH sensor, we are able to determine the N-terminal pKa values of nine tripeptides and also the membrane penetration kinetics of a cell-penetrating peptide. Taken together, these examples demonstrate the applicability of using this unnatural amino acid fluorophore to study pH-dependent biological processes or events that accompany a pH change.

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