Abstract
Heterogeneity of κ-casein prepared by various methods was investigated using zone electrophoresis DEAE-cellulose chromatography, sepharose gel filtration, and isoelectric focusing. Results suggest that all the κ-caseins, regardless of their preparative methods, are more or less heterogeneous and that the heterogeneity depends on at least two factors; molecular size and charge. The result of DEAE-cellulose chromatography shows that κ-casein could dissociate into two components, one of which seemed to be a para-like κ -casein. The para-like κ-casein had been difficult to identify by standard starch gel elec-trophoresis. Therefore, it does not seem to be an impurity, but seems to be one of the components which forms a κ-casein complex. Although random S-S bonds have been thoughta unique cause for tne heterogeneity of κ-casein, variation in the amount of para-like κ-casein may be another cause. The little deviation in the concentration of para-like κ-casein seems to indicate thatthe para-like κ-casein was in the original milk and was not an artifact produced during preparation. It was also found thatκ-casein molecules were the largest and the least heterogeneous when prepared by the urea sulfuric acid method. On the other hand, κ-casein prepared by the calcium ethanol method seemed to be somewhat unfolded into smaller units and to release para-like κ-casein most easily.
