Heterogeneity and fractionation of casein

In 1956, Waugh and von Hippel showed that the a-casein fraction of Hipp et al. contained two proteins, one of which was precipitated by low concentrations of Ca and was called a -casein (s = sensitive) while the other, which was insensitive to Ca, was called xr-casein. a -Casein was later shown to contain two proteins which are now called a i and ag2 Caseins. Thus, bovine casein contains four distinct gene products, designated aji, s2-, and K-caseins which represent approximately 37, 10, 35 and 12% of whole casein, respectively. 

The caseins may be quantified by densitometrically scanning polyacrylamide gel electrophoretograms (section 4.4.1) but more quantitative results are obtained by ion-exchange chromatography using urea-containing buffers. However, it should be realized that the specific absorbance of the individual caseins differs greatly (Table 4.2). 

Distribution Uneven Uneven Very uneven Very uneven Even Even  

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