Fractionation of S-Carboxymethyl- κ-casein and characterization of the components

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1. 1. A method is described for the fractionation of SCM-κ-casein ( S-carboxymethyl- κ-casein) into several fractions by chromatography on DEAE-cellulose in the presence of 20% dimethylformamide as dissociating agent. Essentially the same conditions have been used to fractionate reduced and alkylated whole casein into four main fractions corresponding to α s-, β, SCM- κ- and γ-caseins. 2. 2. Analysis of the fractions of SCM-κ-casein obtained has shown that the carbohydrate of SCM-κ-casein is concentrated in those components which migrate most rapidly during starch-urea gel electrophoresis. The phosphorus of SCM-κ-casein appears to be evenly distributed among the components. 3. 3. The isolation of a major fraction of SCM-κ-casein having virtually no carbohydrate but possessing full micelle-stabilizing ability and rennin sensitivity leads to the conclusion that the carbohydrate plays no significant role in these functions. 4. 4. Examination of the action of rennin (EC3·4·4·3) on a fraction containing no carbohydrate and on another fraction, rich in carbohydrate, leads to the conclusion that the previously observed heterogeneity, with respect to trichloroacetic acid solubility, of the peptide material released by rennin is mainly a result of the heterogeneity of the original κ-casein with respect to carbohydrate content. 5. 5. All the components of SCM-κ-casein give rise to the same two para-derivatives, a major and a minor one, and it is suggested that they arise as a result of the attack of rennin at two different sites in the κ-casein molecule.