Electrophoretic separation of high-molecular hydrophobic proteins: apolipoprotein B and other protein constituents of low-density lipoproteins.

Apolipoprotein B (apoB) and 40 different protein standards were submitted to sodium dodecyl sulfate-polyacrylamide gel electrophoresis under various conditions. The system selected is capable of fractionating well the apoB and its high-molecular-weight species formed after treatment of serum lipoproteins by malonic dialdehyde. The basis for good resolution of protein bands is the use of complex gels combining in one block the areas with constant (T = 3 and 10%) or continuously changing (gradient gel with T = 3-6%) concentrations of acrylamide. The procedure allows one to create the optimal conditions for simultaneous separation of both high- and low-molecular-weight polypeptides. The method was used to determine the relative molecular mass (Mr) of apoB. When apoB was isolated in the presence of proteolytic inhibitors, its Mr was found to be equal to 540,000 +/- 9500 or 500,000 +/- 5700, depending on the linear regression equation applied. The results are in good accordance with values calculated from the amino acid sequence of mature apoB.