Starch Gel Electrophoresis of Various Fractions of Casein

Abstract

Preparations of [alpha]-, [beta]-, gamma-, [lambda] - and K-caseins were compared by electrophoresis in starch gel (cacodylate and veronal buffers containing 5.5 [image] urea) and in free solution. Under the conditions used acid casein separated into at least 17 zones. All fractions of casein contained numerous proteins, but the preparatory procedures brought about considerable enrichment of certain zones while weakening or eliminating others. [alpha]s-Casein appeared to be contaminated with traces of [beta]-, K- and gamma-casein, but the main contaminants were unidentified fractions travelling between [alpha]s- and [beta]-casein. [beta]-Casein was apparently contaminated with traces of gamma-and K-casein and with the unidentified fractions observed in [alpha]s-casein. Our preparations of gamma-casein were heavily contaminated with K-and [beta]-casein, and they contained lesser amounts of [alpha]s-casein and of unidentified fractions. Identification of the K-casein zone was confirmed by zone electrophoresis from urea solution into urea-free gel. K-casein formed a characteristic precipitation zone by electrophoresis in gels containing Ca. Comparison of three K-casein preparations indicated considerable differences both in stabilizing power and in electrophoretic properties. The preparation of K-casein with the least contamination from other casein components appeared to be partially denatured.