Protein optical rotatory dispersion

Tanford (1968) reviewed early studies of protein denaturation and concluded that high concentrations of Gdm-HCl and, in some cases, urea are capable of unfolding proteins that lack disulfide cross-links to random coils. This conclusion was largely based on intrinsic viscosity data, but optical rotation and optical rotatory dispersion (ORD) [reviewed by Urnes and Doty (1961) ] were also cited as providing supporting evidence. By these same lines of evidence, heat- and acid-unfolded proteins were held to be less completely unfolded, with some residual secondary and tertiary structure. As noted in Section II, a polypeptide chain can behave hydrodynamically as random coil and yet possess local order. Similarly, the optical rotation and ORD criteria used for a random coil by Tanford and others are not capable of excluding local order in largely unfolded polypeptides and proteins. The ability to measure the ORD, and especially the CD spectra, of unfolded polypeptides and proteins in the far UV provides much more incisive information about the conformation of proteins, folded and unfolded. The CD spectra of many unfolded proteins have been reported, but there have been few systematic studies. 

Bonar, L. C., Mechanic, G. L., Glimcher, M. ]. Optical rotatory dispersion studies of the neutral soluble proteins of embryonic bovine enamel. J. Ultrastruct. Res. 13, 296 (1965)... 

Protein Conformation Optical Rotatory Dispersion and Circular Dichroism... 

Jaenicke and Lauffer105,145,146 have found changes in the optical rotatory dispersion when the tobacco mosaic virus polymerizes. Lauffer105 interprets this observation as a change of the protein conformation effected by the different structures during exposure on all sides to water or in contact with other protein molecules. 

Recently, another red protein Buchanan, Lovenberg, and Rabinowitz 32) Mortenson 72) has been isolated in crystalline form from C. pasteurianum and certain of its properties determined Lovenberg and Sobel 67)). Lovenberg and Sobel 67) named it rubredoxin because of its color and properties of an electron carrier. They showed rubredoxin differed from ferredoxin in absorption spectrum, composition and redox potential. Rubredoxin contained no inorganic sulfide the recent demonstration 49) of the similarity of the optical rotatory dispersion spectra of rubredoxin and bacterial ferredoxin makes a further comparison of the properties of these proteins particularly interesting. 

Vallee, B. L. and D. D. Ulmer Optical rotatory dispersion of iron proteins. In Non-Heme Iron Proteins Role in Energy Conversion, A. San Pietro, ed., Antioch Press, Yellow Springs, Ohio, pp. 43—68 (1965). 

Studies of the optical rotatory dispersion of the transferrins and their metal complexes have not only shown important differences between the two forms of the proteins but also have afforded penetrating insight into the possible groups involved in chelation of the metal and in the structure of the complex (128, 129). These authors studied both chicken ovotransferrin and human serum transferrin and obtained essentially identical results with both proteins. Metal-free ovotransferrin had a plain negative rotatory dispersion between 300 and 675 mjj. with a specific rotation,... 

The configuration of the localized iron binding area in adrenal and testis non-heme iron proteins could be extensively studied by measuring the optical rotatory dispersion (ORD) and circular dichroism (CD). The ORD properties of various non-heme iron containing proteins were reported by Vallee and Ulmer (67). 

Optical rotatory dispersion and circular dichroism (83, 84) can often be of great value, and the spectra are particularly sensitive to the conformation of the protein. Much work remains to be done in this field before the results can be definitely interpreted in terms of the electronic structure of the metal. Magneto-optical rotation and magnetic circular dichroism (MOR and MCD), which are beginning to be applied to porphyrins and haemoproteins, offer much greater promise (30, 85). 

The secondary and tertiary structure of a partially purified 7S globulin was examined by Fukushima (7) based on optical rotatory dispersion, infrared and ultraviolet difference spectra. Antiparallel (5 -structure (352) and random coil (60%) predominated with only 5% helical structure present. The contribution of the three structures was calculated from molecular ellipticity values obtained by circular dichroism (11) and from the Moffitt parameters in ORD (11, 12). Between 210 and 250 nm, the experimental CD curve for the 7S protein was similar to the CD curve computed from ORD Moffitt parameters with the major dissimilarity occurring at 208-213 nm. 

Blout ER, Carver JP, Shechter E (1967) ORD of Polypeptides and Proteins. In Snatzke G (ed) Optical Rotatory Dispersion and Circular Dichroism in Organic Chemistry. Heyden, London, p 224... 

ACS = anunonium (-l-)-DlO-camphorsulfonate BSA = bovine serum albumin CD = circular dichroism CT = charge transfer hCCS = human copper chaperone for superoxide dismutase hSCAN = human soluble calcium-activated nucleotidase-1 LMCT = ligand-to-metal charge transfer METP = miniaturized electron transfer protein MECT = metal-ligand charge transfer ORD = optical rotatory dispersion SODs = superoxide dismutases tCCS = tomato copper chaperone for superoxide dismutase UTP = uracil triphosphate. 

Optical Rotatory Dispersion of Polypeptides and Some Proteins "... 

More recently, Doty and co-workers (Doty, 1959) have found that a large number of globular proteins are directly soluble in the solvent 2-chloroethanol. While the apparently unique solubilizing power of this substance is probably attributable to the HCl present in the unstable solvent, some very significant measurements of the optical rotatory dispersions of proteins in a pure weakly protic nonaqueous solvent were made as a result of this discovery. In all cases studied, proteins exhibited larger, often substantially larger, values of —ho in 2-chloroethanol than in HjO (Table VII). These effects are reversible with change of solvent. 

A solvent which has been foimd to be of great interest in connection with protein conformation studies is ethylene glycol. Sage and Singer (1958, 1962) have investigated in some detail the properties of RNase in pure ethylene glycol, containing added neutral electrolyte. They examined the ultraviolet absorption spectrum, the ionization behavior of the tyrosine residues by spectrophotometric titration experiments, and the optical rotatory dispersion of the system. 

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