The ultraviolet absorption spectra of proteins.

The absorption spectra of proteins have been made the subject of considerable study. For the greatest number of proteins there has been demonstrated a broad band with a peak at about 280 rnp and a minimum, on the short wave-length side, at about 250 m,u (1). From quantitative studies of simple proteins, this band could be correlated with the presence of tyrosine, tryptophan, and phenylalanine (2). A number of proteins exhibited absorption bands at wave-lengths above 280 rnp that could be interpreted in terms of a non-proteinaceous chromophore. Similarly, nucleoproteins show a maximum in the region of 260 rnp, which is associated with the presence of purine and pyrimidine nuclei (3). Most of the curves reported for proteins end at about 235 rnp on the short wave-length side of the main 280 mp peak, and, in this region, the absorption curves rise rapidly. Such a steep rise has led several investigators to assume that at shorter wave-lengths there is a region of continuous or end-absorption (4, 5). The specific structure of a protein that distinguishes it from other compounds is the presence of a large number of peptide bonds. Ley and Arends (6) and Rusoff et al. (7) studied the ultraviolet, absorption spectra of fatty acids, esters, anhydrides, and acid chlorides, and demonstrated that broad bands do exist in the region of 200 m/l. It seemed, therefore, that studies in the region below 240 rnp would be of interest.