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Updated: Feb 19, 2026

Chemical Modification of the Tryptophan Residue in a Recombinant Ca2+-ATPase N-domain for Studying Tryptophan-ANS FRET
Published on: October 9, 2021
Photon Antibunching Reveals Static and Dynamic Quenching Interaction of Tryptophan with Atto-655
Arjun Sharma1,2, Jörg Enderlein3, Manoj Kumbhakar1,2
1Radiation & Photochemistry Division, Bhabha Atomic Research Center , Mumbai 400085, India.
Abstract:
Fluorescence correlation spectroscopy (FCS) of photoinduced electron transfer (PET) between the dye Atto-655 and the amino acid tryptophan has been extensively used for studying fast conformational dynamics of small disordered peptides and proteins. However, a precise understanding of the quenching mechanism and its exact rates that would explain ensemble as well as single-molecule spectroscopy results is still lacking. In this contribution, a general unified model for intermolecular PET between Atto-655 and tryptophan is developed, which involves ground-state complex formation, quenching sphere of action, and dynamic quenching at the single-molecule level. We present measurements of fluorescence antibunching, fluorescence lifetime, and steady-state fluorescence intensity and absorbance and demonstrate that our model is capable to describe all results in a global and coherent manner.
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