Absorption spectra of proteins

UV or visible absorption spectra of proteins and nucleic acids are very simple, with either one or two absorption peaks. Examples are shown in Figure 16.14. 

G. H. Beaven and E. R. Holiday, Ultraviolet absorption spectra of proteins and amino acids, Adv. Protein Chem. 7, 319-386 (1952). 

A number of investigators have studied the effect of ozone on the ultraviolet absorption spectra of proteins and amino acids. A decrease in the absorption of 280-nm light in a number of proteins was originally reported ly Giese et aV to be a consequence of ozone exposure they suggested that this was due to an interaction of ozone with the ring structures of tyrosine and tryptophan. Exposure of a solution of tryptophan to ozone resulted in a decrease in 280-nm absorption, whereas the extinction coefficient of tyrosine increased. Similar results with tyrosine were reported by Scheel et who also noted alterations in the ultraviolet spectra of egg albumen, perhaps representing denaturation by ozone. 

Giese, A. C., H. L. Leighton, and R. Bailey. Changes in the absorption spectra of proteins and representative amino acids induced by ultraviolet radiations and ozone. Arch. Biochem. Biophys. 40 71-84, 1952. 

Figure 3-14 shows the spectra of N-acetyl ethyl esters of all three of the aromatic amino acids and of cystine. To a first approximation, the absorption spectra of proteins can be regarded as a summation of the spectra of the component amino acids. However, the absorption bands of some residues, particularly of tyrosine and tryptophan, are shifted to longer wavelengths than those of the reference compounds in water. This is presumably a result of being located within nonpolar regions of the protein. Notice that the spectra for tyrosine, phenylalanine, and cystine in Fig. 

The lanthanides modify the UV absorption spectra of proteins when aromatic chro-mophores are present at the binding site. Sharp maxima at 245 and 295 nm in the difference spectrum of transferrin saturated with Tb3+ ion as opposed to that of metal free protein were observed [20]. The shape of the spectrum is suggestive of lanthanide induced... 

The absorption spectra of proteins and polypeptides are now much better understood as a result of the vibrational analyses given by Miyazawa (1960, 1962, 1963), but it is still true that structures are more often used to test the interpretation of spectra rather than the reverse. Transition moment directions and coupling effects, however, are now sufficiently well understood for infrared dichroism measurements to provide at least a semiquantitative evaluation of some features of a model. 

In the early papers on the ultra-violet absorption spectra of proteins, the absorption in the 250-280 m/x region had been attributed to the peptide linkage, —CO—NH1 . But it is now established beyond doubt that amides absorb in the far ultra-violet region (see Chapter 3). Thus the absorption of proteins in the near ultra-violet region can only be due to the component aromatic amino acids . 

Ultraviolet Absorption Spectra of Proteins and Amino Acids... 

IX. Analysis of the Absorption Spectra of Proteins in Terms of Tyrosine and... 

The alterations in the absorption spectra of proteins at high pH values were first ascribed to ionization of the tyrosine residue by Stenstrom and Reinhard (1925). However this explanation seems to have been accepted with some reserve, as the arguments for it have been frequently restated, most recently by Sizer and Peacock (1947) who give references... 

Figure 1.7. Absoqition spectra of tiyptophan, tyrosine and phenylalanhi Wctbufcr, D. B., 1962, Ultraviolet absorption spectra of proteins and a Protein Ghent. l7.303-39a...

J. W. Ellis and J. Bath, Modifications in the Near Infra-Red Absorption Spectra of Protein and of Light and Fleavy Water Molecules When Water Is Bound to Gelatin,/. Chem. Phys., 6,723 (1938). 

The absorption spectra of proteins in the ultraviolet above 2500 A is due mainly to the aromatic amino acids. Quantitative measurements, recently reviewed in this series (Beaven and Holiday, 1952) show that the position and shape of the bands are very similar or identical in the free... 

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