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A method is described for the spectrographic analysis of conjugated proteins, formed by the interaction of serum proteins with the isocyanates of certain polynuclear aromatic hydrocarbons. The method makes possible the determination of the number of hydrocarbon groups introduced into each protein molecule, provided the hydrocarbon chromophoric has maxima at wave-lengths greater than 3250A. At wave-lengths less than 3250A, where the chromophoric groups of the normal protein also absorb, the total absorption is shown not to be equivalent to the sum of the absorptions of the several chromophoric groups involved. The spectra of binary solutions of the unconjugated protein and a simple, water soluble, compound containing the hydrocarbon chromophore, exhibit deviations from the calculated summation spectra which are of a similar character to those exhibited by the conjugated proteins. It is shown that the scattering of light by the protein molecule plays no direct part in this effect. The absorption spectra of mixtures of l-tyrosyl-l-tyrosine and horse serum albumin do not exhibit abnormal behavior; the observed spectra are closely similar to those calculated from the summation of the spectra of the two solutes. Although the abnormalities in the spectra of protein solutions do not appear to be of a general character, attention is drawn to the possibility that effects of this nature may occur in other solutions containing proteins. Care must be exercised, therefore, in the application of spectrophotometry and colorimetry to the analysis of substances in the presence of proteins.
© 1943 Optical Society of America
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