Optical rotatory dispersion of 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. 

Jirgensons, B. Optical rotatory dispersion of proteins and other macromolecules. Berlin-Heidelberg-New York Springer 1969. 

Jirgensons, B. (1969). Optical Rotatory Dispersion of Proteins and Other Macromolecules. Springer-Verlag, Berlin and New York. 

Adler AJ, Greenfield NJ and Fasman GD (1973) Circular dichroism and optical rotatory dispersion of proteins and polypeptides. Methods in Enzymology 11 part D 675-735. 

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,... 

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

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. 

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. 

Let us begin by examining the optical rotatory dispersions of two typical synthetic pol3q>eptides and a well-studied protein, as illustrated in Fig. 1. The spectral range along the abscissa is that usually available for polarime-try, while the ordinate is the reduced mean residue rotation, a quantity that will be defined by Eqs. (1) and (4). For each of the three substances, two different conformations are represented. Those denoted by PEG refer to poly- -benzyl-L-glutamate, which exists as a flexible, random coil in... 

The optical rotatory dispersions of all native globular proteins thus far measured have obeyed the simple Drude equation in the spectral range usually encompassed, 350-600 m/i. In most cases, K values vary from 230 to 280 m/i, although a number of proteins have values below 230 m/i and some as low as 180 m/ . Optical rotations, which are usually reported as the specific rotations at 589 m/t, range from about —20 to —80°. Upon de-naturation, all dispersions remain simple, but values shift to the more narrow range of 210-230 m/i and the specific rotation becomes more levorotatory to a range of about —80 to —120°. 

Absorption, circular dichroism and optical rotatory dispersion of polypeptides, proteins, prosthetic groups and biomembranes... 

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)... 

---