Peptide bonds, ultraviolet absorption

The ultraviolet spectra of proteins can for present purposes be divided into three regions above 2500 A, between 2500 and 2100 A, and below 2100 A. We can paraphrase this division by calling the first region simple —only a few absorbers and easily sorted out calling the second region complex because of the multiplicity of the contributions to absorptivity and calling the third complex but exciting, because of the peptide-bond absorption and its conformation-dependence. 

Since the dispersive properties of helices in what will be taken as the standard sense, now known to be right-handed as in myoglobin, have been the most thoroughly studied and since a case can be made that it is the predominant sense in proteins, this review will focus on the capacity of optical rotatory methods to discern mixtures of this conformation with disordered regions. It will discuss the manner in which theoretical considerations have provided the forms into which rotatory data are currently cast, the calibration of their constants by studies of synthetic polypeptides in known conformation, and then the application of these equations and scales in the structural interpretation of the rotatory dispersion of proteins. This pattern of analysis will undoubtedly undergo refinement and revision as these methods are applied to new species of polypeptide and protein in concert with other means of conformational assignment. In particular, an extension of the spectral range of measurement toward optically active absorption bands in the far ultraviolet can be expected to yield new information about the rotatory power of the peptide bond and thus enhance the interaction of theory and observation that has already proved fruitful. 

Peptide bonds enable proteins and peptides to be directly detected by ultraviolet (UV) radiation, at 200-220 nm, where the absorption is proportional to the number of... 

VIII. The Ultraviolet Absorption Spectrum of the Peptide Bond and of the Polypeptide Fabric. 352... 

Using ultraviolet/visible (UV/Vis) absorption spectroscopy, it is possible to measure the protein concentration using Beer s Law A = e c, where A is the measured absorbance of a solution, e is the absorptivity of the protein, is the pathlength of the cell used to determine the absorbance, and c is the protein concentration. Proteins typically exhibit two strong, broad absorption bands in the UV/Vis part of the spectrum. The first and most intense band is centered at 214 nm and arises from absorption of light by the peptide backbone. The second absorption band is typically found at 280nm. This band arises from absorbance from the aromatic side chains of Trp, Tyr, and Phe. Disulfide bonds may exhibit weak absorption in this range as well. 

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