| dc.description.abstract | A new method has been developed for estimating the extinction coefficient for a protein. The only information that is needed is the amino acid composition of the protein, and this is readily available if the gene coding for the protein has been sequenced. This method will allow extinction coefficients to estimated with an accuracy of better than 4% for most proteins. This will allow much more quantitative studies than had been possible in the past with the many proteins that can be obtained in only small amounts. A nonlinear least squares analysis was used to calculate the "best" extinction coefficients over the wavelength range 272 nanometers (nm) to 286 nm for the chromophores tyrosine (Tyr), tryptohan (Trp) and cystine (-S-S-). These values were then used to estimate the extinction coefficients for 17 proteins, yielding estimates that were on average within 3.4% of the experimental values. For comparison, the extinction coefficients for the model compounds N-acetyl-Tyr-ethyl ester (N-Ac-Tyr-OEE), N-acetyl-Trp-ethyl ester (N-Ac-Trp-OEE), and oxidized glutathione were determined over the same wavelength range in the following solvents: water, 6 M guanidinium hydrochloride (GdnHCl), 8 M urea, 1-propanol, and formamide. It was found that Trp, Tyr, and -S-S-in proteins resemble these model compounds in 6 M GdnHCl and 8 M urea rather than in water or in the more nonpolar solvents 1-propanol and formamide. The estimates for protein extinction coefficients based on model compounds in 6 M GdnHCl and 8 M urea were on average within 3.8% and 3.9%, respectively, of the experimental values. | en |
