Fractionation of Skimmilk Proteins by Sephadex Gel Filtration

Abstract

Summary Sephadex G-75 and G-100 gel filtration was employed to determine the protein particle size distribution in skimmilk and ultracentrifugal serum as affected by heat, dialysis, and oxalate-solubilization. Sephadex G-75 failed to fractionate skimmilk proteins satisfactorily, but yielded two partially separated protein components. Sephadex G-100 fractionated unheated skimmilk into four heterogeneous components with about 52, 11, 10, and 26% of the total elution pattern area in each of these components in the order of elution. Oxalate solubilization altered the gel filtration properties of the proteins to a much greater extent than dialysis against phosphate buffer alone. Heating skimmilk (74–90.5 C—10 min) caused two major alterations in the Sephadex patterns: (a) an increase in the largest-sized protein component at the expense of the serum proteins and (b) an increase in the nonprotein nitrogen component. Heating prevented the alteration of the proteins by oxalate-solubilization, as was achieved with the unheated systems.