ELECTROPHORETIC SYSTEMS FOR PREPARATIVE FRACTIONATION OF PROTEIN PRECURSORS OF BIOACTIVE PEPTIDES FROM COW’S MILK

Abstract

The article considers the possibility of obtaining purified fractions-precursors of bioactive peptides from milk proteins by the method of preparative electrophoresis. To choose an electrophoretic system, a comparative study has been carried out of four methods of electrophoresis in polyacrylamide gel that are used to analyse milk proteins (disc-electrophoresis without disaggregating agents, and disc-electrophoresis in the presence of sodium dodecylsulfate in homogeneous and gradient gel, and electrophoresis in homogeneous gel with urea). Electrophoresis of the total milk protein has shown that none of these systems allows separating effectively all protein precursors of bioactive peptides. The next stage was obtaining two main groups of milk proteins – caseins and serum proteins for electrophoretic fractionation. With the help of analytical electrophoresis, it has been established that each of the obtained groups had a typical proteins composition. Then, the proteins groups obtained were fractionated by preparative electrophoresis using the four electrophoretic systems listed above. In this case, the casein proteins that differ in the primary structure (αS1-, αS2-, β-, and ϰ-caseins) can be effectively separated by preparative electrophoresis on the basis of a homogeneous gel system in the presence of urea. The composition of this electrophoretic system was simplified. Unlike the analytical variant of a homogeneous polyacrylamide gel system, the toxic 2-mercaptoethanol was excluded, and the urea concentration was reduced. For the fractionation of serum proteins, a disc-electrophoresis without disaggregating agents can be used as a basis. It allows obtaining the main precursors of bioactive peptides from milk serum proteins: β-lactoglobulin, α-lactalbumin, serum albumin, and immunoglobulins. The protein precursors obtained by preparative electrophoresis were used to develop the biotechnology of obtaining bioactive phosphopeptides and inhibitors of the angiotensin-converting enzyme.