Abstract
Only four intrinsic protein chromophores absorb light significantly in the near-UV region of the spectrum (340-255 nm): the side chains of Trp, Tyr, Phe, and cystine (note: cysteine residues make no significant contribution). The absorption spectra are shown in Fig. 1. Although several amino acid side chains (notably Tyr, Trp, Phe, His, and Met) absorb light strongly in the far-UV region (below 250 nm), the most important contributor here is the peptide bond (amide chromophore), with n ?π * and π ? π * transitions at approx 220 nm and approx 190 nm, respectively. The contribution of any individual chromophore to the total absorbance of the protein will depend, to some extent at least, upon its environment. The experimentally measured parameter, the absorbance A is related to the molar extinction coefficient, εM (M-1cm-1), the path length l (cm), and the protein concentration C (M) by the Beer-Lambert law A = εM.C.l.
Absorption spectra of tryptophan (?), tyrosine (Δ), phenylalanine (O), and cystine (..v) recorded in 10 mM phosphate buffer (pH 7.0). The spectrum for phenylalanine has been multiplied by 10 for clarity.
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Martin, S.R., Bayley, P.M. (2002). Absorption and Circular Dichroism Spectroscopy. In: Vogel, H.J. (eds) Calcium-Binding Protein Protocols: Volume 2: Methods and Techniques. Methods in Molecular Biology™, vol 173. Springer, Totowa, NJ. https://doi.org/10.1385/1-59259-184-1:043
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DOI: https://doi.org/10.1385/1-59259-184-1:043
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