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Charged amino acids absorb past 250 nm
A 67-residue protein with no aromatic side chains still absorbs from 250 to 800 nm because Lys/Glu charge-transfer transitions create Protein Charge Transfer Spectra.
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What is ProCharTS?
Protein Charge Transfer Spectra: 250–800 nm absorption from charged amino-acid CT transitions.
Source: Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein · DOI · quote verified
Why is α3C a useful spectroscopic model?
It is monomeric and has no aromatic amino acids, so aromatics cannot explain the UV-Vis.
Source: Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein · DOI · quote verified
What fold does α3C have?
A three-helix bundle (NMR).
Source: Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein · DOI · quote verified
How charged is the α3C sequence?
54% charged residues: 17 Lys, 17 Glu, 2 Arg.
Source: Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein · DOI · quote verified
What ε did they report at 250 nm?
7338 ± 191 M−1 cm−1.
Source: Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein · DOI · quote verified
How far does the absorption tail extend?
Through the visible to 800 nm.
Source: Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein · DOI · quote verified
Which groups participate in the CT transitions?
Lys NH3+ / Glu COO− side chains and the peptide backbone.
Source: Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein · DOI · quote verified
What Lys–Glu distances modulate the spectrum?
Spatially proximal 4–6 Å contacts from the fold.
Source: Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein · DOI · quote verified
How did they perturb the spectrum experimentally?
Temperature and pH changes that alter the fold and charged-group separations.
Source: Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein · DOI · quote verified
What mass confirmed purified α3C?
7462.883 Da by electrospray MS.
Source: Near UV-Visible electronic absorption originating from charged amino acids in a monomeric protein · DOI · quote verified