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Journal of Dairy Science Vol. 44 No. 6 1016-1024
© 1961 by American Dairy Science Association ®
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Paper Electrophoresis of Casein. I. The Use of Buffers Containing Urea1

L. M. Libbey and U. S. Ashworth

Department of Dairy Science, Washington State University, Pullman

ABSTRACT

A study has been made of the paper electrophoresis of casein and casein fractions in Veronal buffers containing urea levels from 0 to 7.0 M. A method using the Sharples supercentrifuge was developed that permits the isolation of whole {kappa}-casein from {alpha}-casein without the need for an ultracentrifuge. It was found that whole {kappa}-casein migrates in the {alpha}, or fastest-moving peak, when the urea level is 0–2.5 M, but migrates in the ß, or second-fastest peak, when the urea level is about 6.0–7.0 M. Veronal buffers containing urea levels of about 2.5 M or greater (pH ~ 8.9, {Gamma}/2 0.050) permit the resolution of casein into at least six components; four of these components migrate slower than ß-casein. {kappa}-Casein could not be completely resolved from the other components of whole casein, although at 4.8 M urea the {kappa}-casein formed a peak between {alpha}s- and ß-casein. Whole {kappa}-casein became increasingly heterogeneous as the urea level of the buffer was increased. Whole casein contained approximately 39% {alpha}s-casein, 11% {kappa}-casein, 43% ß-casein, and 7% minor components.

The use of urea in electrophoresis buffers for casein appears promising as a high order of resolution is attained. The effect of urea level on the migration of {kappa}-casein appears important in quantitative studies on the relative abundance of casein fractions.

FOOTNOTES

1 Scientific Paper No. 2062, Washington Agricultural Experiment Station, Pullman.






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