Paper Electrophoresis of Casein. I. The Use of Buffers Containing Urea

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 supereentrifuge was developed that permits the isolation of whole K-casein from a-casein without the need for all ultracentrifuge. It was found that whole K-casein migTates in the a, or fastest-moving peak, when the urea level is 0-2.5 M, but migrates in the t~, 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, F/2 0.050) permit the resolution of casein into at least six components; four of these components migrate slower than E-casein. K-Casein could not be completely resolved from the other components of whole casein, although at 4.8 M urea the K-casein formed a peak between a s-and E-casein. Whole ~-easein became increasingly heterogeneous as the urea level of the buffer was increased. Whole casein contained approximately 39% as-casein , 11% ~-casein, 43% fl-casein, and 7% minor components.