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Journal of Dairy Science Vol. 45 No. 7 811-816
© 1962 by American Dairy Science Association ®
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Application of Polarization of Fluorescence Technique to Protein Studies. I. The Rotatory Properties of ß-lactoglobulin1

C. V. Morr, Q. Van Winkle and I. A. Gould

Departments of Dairy Technology and Chemistry, The Ohio State University, Columbus

ABSTRACT

A study was conducted using the polarization of fluorescence method to characterize ß-lactoglobulin. The method involved forming a fluorescent dye conjugate of the protein molecule with a dye molecule (1-dimethylaminonaphthalene-5-sulfonyl chloride) which imparted fluorescent properties to the conjugate. Only minor alteration in the physical properties of the protein was produced by the conjugation process.

Curves of reciprocal polarization vs. T/{eta} for ß-lactoglobulin yielded an average slope of 1.02 x 10–4 at 0.02 ionic strength and 0.72 x 10–4 at 0.10 ionic strength. The apparent molecular volume of a spherical protein molecule, having the same relaxation time as the slightly elongated ß-lactoglobulin molecule, was 98,310 cm3 at 0.10 ionic strength and 64,580 cm3 at ionic strength 0.02. The mean harmonic relaxation time for ß-lactoglobulin was 6.85 x 10–8 sec at 0.02 ionic strength and 10.91 x 10–8 sec at 0.10 ionic strength. Addition of sucrose to protein solutions to increase the viscosity and, thereby, reduce the rate of rotatory diffusion of the fluorescent ß-lactoglobulin molecule, resulted in substantial reduction in the apparent molecular volume.

FOOTNOTES

1 Article 262, Department of Dairy Technology. Supported in part by University grants-in-aid and by a grant from the National Institutes of Health (U. S. Public Health Service).






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