An Analysis of Perturbations in the Ultraviolet Absorption Spectra of Proteins and Model Compounds.

It is shown that the perturbation of the ultraviolet absorption spectra of the tyrosine and tryptophan chromophores in aqueous solutions by addition of solvents of lower polarity leads not only to red shifts but also to changes in peak intensity, and oscillator strength. The effect is much greater in tyrosine than in tryptophan, and can be as large as 30% (transfer from water to ethanol). It is shown that observed difference spectra can be reasonably reproduced by the addition of two calculated curves, one corresponding to a shift, the other to a change in intensity, i. e. an admixture of shift difference spectrum and absolute spectrum. Similar intensity changes are seen to accompany the denaturation of several proteins. The changes of the characteristic parameters of difference spectra with the concentration of perturbant are analyzed. The relation between the difference spectra generated by aromatic chromophores near 230 mμ. and those m the 280 mμ. region are considered, and their relative magnitudes have been estimated for a variety of perturbants. It is shown that in denaturation. of a number of proteins, the difference spectra near 230 mμ cannot be satisfactorily accounted for solely in terms of the model compounds containing aromatic chromophores. Possible contributions to difference spectra of proteins in this region are considered. [ABSTRACT FROM AUTHOR]