A simple ultraviolet spectrophotometric method for the determination of protein.

Publisher Summary This chapter deals with the absorption spectra of proteins and amino acids The colored proteins are conjugated proteins in which the protein carrier is colorless This transparency of protein solutions extends into the ultraviolet region of the spectrum and many proteins do not absorb radiation of longer wavelength than 2500 Ǻ The essential protein fabric, consisting of a peptide chain in various forms, is not responsible for absorption at longer wavelengths In case of fibrous proteins, there is some evidence that the peptide fabric is responsible for absorption in this region Many proteins absorb in this region This absorption is due to the aromatic amino-acids present in the protein The advent of quantitative methods of spectrophotometry is the basis of a method of determining tyrosine and tryptophan in proteins The striking property of proteins is their transparency, indicating a high degree of electronic saturation The configurational stability of the protein molecule depends entirely on extra-valence forces and not on unsaturation, which would result in high absorption in the ultraviolet The absence of such rigidifying bonds endows the protein with its unique characters of plasticity, while the number-sequence of side chains gives its chemical constancy These two properties allow these molecules to be arranged in large polymorphic masses to form a matrix fabric of recurrent pattern in media, which are essentially aqueous The material reviewed is principally derived from the study of homogeneous absorbing systems, in which the inhomogeneity is finer in grade by several orders than the dimensions of the exploring light beam

Ultraviolet absorption spectra of proteins and amino acids.

Publisher Summary This chapter reviews that the simplest way of accounting for the absorption spectrum of a protein is as the sum of the spectra of its components. This gives results which are often good approximations to the observed protein spectrum. The assumption of additivity is basic for useful analytical applications of spectral measurements. It discusses that in another perspective, the failure of perfect additivity of the component absorptivities affords the possibility of obtaining structural information about proteins. The absorptivity of the peptide bond can change by as much as a factor of two with a change in the conformation of a peptide chain. Since the absorptivity of aromatic side chains is much less sensitive to environmental change, correspondingly, more sensitive techniques are required to measure the small changes which do occur. The nature and limitations of the structural information resulting from both peptide-bond and side-chain absorption are discussed. Absorption spectra can occasionally be a useful tool in the identification of unusual structural features in proteins and polypeptides. Several such applications are also explained in this chapter.

Erwin Mosovich

Papers

The ultraviolet absorption spectra of proteins