Fractionation and Some Properties of κ-Casein Variants

Abstract

The whole [eta] -caseins A and B are fractionated by column chromatography on diethylaminoethyl (DEAE) cellulose with buffer solutions containing 2-mercapto-ethanol. The contents of sialic acid, P and cystine were determined. Their sensitivity to rennin and the ability to stabilize [alpha] s1-casein against Ca2+-ions were measured. Only differences in sialic acid content were found M the fractions of 1 variant. These observations are consistent with the model of the [eta] -casein molecule, developed by MacKinlay and Wake. Amino-acid analysis of the main fractions revealed that an aspartic acid residue in [eta] -casein A (0.60) was replaced by an alanine residue in [eta] -casein B (0.52). The peptide chain of [eta] -casein B contains 2 more amino-acids than n -casein A.