0-Lactoglobulin refractive index

A light-scattering study of this nature has been carried out on solutions of /J-lactoglobulin A (0-A) dissolved in mixtures of water with 2-chloroethanol in the presence of 0.02M NaCl and 0.01 M HC1. 2-Chloro-ethanol is known to be a structure-forming protein denaturant and can be expected to interact with proteins freshly distilled, its refractive index at 436 m/x is 1.447, different from that of water, 1.340. This results in a large value of dn/dCi. 

The molar refractions of the amino acids were determined by measurements on their aqueous solutions and the expanded Lorenz-Lorentz equation. The refractive indices of a number of proteins were calculated from their amino acid compositions and the values for the refraction of the amino acid residues. These calculated results are in good agreement with those experimentally determined, demonstrating that refractive index is a unique characteristic of a protein. A comparison of the refractive index of heat denatured /3-lactoglobulin with the native protein demonstrated that changes in structure produced a small change in refractive index, not associated with a change in volume. 

The thickness and the refractive index of the adsorbed protein layer were determined by ellipsometry [7]. The adsorbed mass, r, was calculated according to Cuypers et al. (81. The values used for the molar weight/molar refractivity were 4.10 and 4.17 g/ml and for the partial specific volume 0.751 and 0.750 ml/g for jS-lactoglobulin and ovalbumin, respectively. The change in electrode potential, AE, was... 

The adsorbed amounts of ff-lactoglobulin, with plateau values of the thickness and of the refractive index, on hydrophobic and hydrophilic chromium surfaces, respectively, are shown in figures 1 and 2. The potential changes are also shown in these figures. The corresponding curves were recorded for ovalbumin and are shown in figures 3 and 4. 

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