The molar absorption coefficient, E, of a protein is usually based on concentrations measured by dry weight, nitrogen, or amino acid analysis. The studies reported here suggest that the Edelhoch method is the best method for measuring E for a protein. (This method is described by Gill and von Hippel [1989, Anal Biochem 182:3193261 and is based on data from Edelhoch [1967, Biochemistry 6:1948-19541.) The absorbance of a protein at 280 nm depends on the content of Trp, Tyr, and cystine (disulfide bonds). The average E values for these chromophores in a sample of 18 well-characterized proteins have been estimated, and the E values in water, propanol, 6 M guanidine hydrochloride (GdnHCI), and 8 M urea have been measured. For Trp, the average E values for the proteins are less than the E values measured in any of the solvents. For Tyr, the average E values for the proteins are intermediate between those measured in 6 M GdnHCl and those measured in propanol. Based on a sample of 116 measured t values for 80 proteins, the t at 280 nm of a folded protein in water, t(280), can best be predicted with this equation:

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pro.5560041120

How to measure and predict the molar absorption coefficient of a protein.

The precision of ultraviolet absorption measurements in the Schmidt-Thannhauser procedure for nucleic acid estimation

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.

Ultraviolet spectra Of Proteins and Amino Acids

(1974). Aromatic Contributions To Circular Dichroism Spectra Of Protein. CRC Critical Reviews in Biochemistry: Vol. 2, No. 1, pp. 113-175.

Aromatic contributions to circular dichroism spectra of proteins.

Publisher Summary This chapter discusses the process of isolation, chromatography, structure, and molecular and catalytic properties of bovine pancreatic ribonuclease. At present there are three simple and widely used chromatographic procedures: (1) Hirs base their method on the carboxyl ion exchange resin IRC-50 with 0.2 M phosphate buffer pH 6.45 as the eluting medium. The principal active component of the enzyme preparation is well retarded and is universally referred to as ribonuclease-A. Several poorly resolved faster running peaks are usually seen, the area having the highest activity and running closest to A normally being called ribonuclease B. The ratio of A to B varies with the preparation but may be as high as 10 to 1. (2) Taborsky has described a system based on carboxymethyl cellulose as the exchanger operated in Tris buffer at pH 8 with a sodium chloride gradient. The excellent and adjustable resolution of this system is frequently useful. The principal peak, labeled D by Taborsky, is indistinguishable from ribonuclease-A in the IRC-50 system. (3) Crestfield found chromatography on sulfoethyl Sephadex valuable. Ribonuclease-A may develop heterogeneity during lyophilization and storage. Aggregation appears to occur. A careful study of the preparation problem has been made by Crestfield by using chromatography on Sephadex G-75, and sulfoethyl Sephadex C-25 as well as IRC-50. These authors recommended that RNase-A be stored as a solution in phosphate buffer at –20°C, that salts be exchanged by dialysis or pre-equilibrated Sephadex columns, and that concentration, if necessary, be effected by ultrafiltration. If lyophilization is necessary, it should be carried out from dilute salt-free solution to minimize aggregate formation. The aggregates can be converted to monomers by heating to 60° for a few minutes at neutral pH. The properties of the ribonuclease dimer are also discussed in the chapter.

24 Bovine Pancreatic Ribonuclease

Interpretation of the ultraviolet spectral changes of proteins.

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Interpretation of the ultraviolet spectral changes of proteins.