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A Comparison of Some of the Chemical and Physical Properties of -Casein and Immune Globulins of Milk¹

Department of Food Technology, University of Illinois, Urbana

ABSTRACT

To identify the slowest component in the electrophoretic pattern of skimmilk at pH 8.7 and to investigate further the chemical and physical properties of -casein and the immune globulins, these proteins were isolated from milk and colostrum. Phosphorus analyses indicate a distinct difference between -casein and immune globulins. In veronal buffer at pH 8.7, µ = 0.1, the electrophoretic mobilities of -casein and pseudoglobulin are the same. In glycine hydrochloride buffer pH 2.3, µ = 0.1, the three proteins have different electrophoretic mobilities, but a mixture of -casein-euglobulin interacts, the extent depending on the time of storage at 4° C. While -casein is electrophoretically homogeneous in glycine hydrochloride buffer at pH 2.3 and 3.25 and µ = 0.1, it is heterogeneous in comparable sodium lactate buffers, due to interactions with the lactate ion. All three proteins contribute to the area of the slowest-moving component in the electrophoretic pattern of skimmilk at pH 8.7. They are heterogeneous in the ultracentrifuge. The molecular weight calculated for the major components of -casein varied with pH; whereas, the frictional ratios were the same in veronal and glycine hydrochloride buffers but decreased in sodium lactate buffer. The molecular weights of euglobulin and pseudoglobulin were not pH-dependent, but their frictional ratios increased with decreasing pH values.

¹ Taken from the thesis of G. K. Murthy, presented in June, 1956, to the University of Illinois, in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

² Present address, Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio.