Quantitative measurement of lipoprotein surface charge by agarose gel electrophoresis

The electrophoretic mobilities of low density lipoprotein (LDL) and six pure proteins in a 0.5% agarose gel have been compared to literature electrophoretic mobility values determined by the Tiselius moving boundary method. There is a strong correlation (r = 0.99) between the electrophoretic mobilities determined by the two techniques. The electrophoretic behavior of charged particles smaller than very low density lipoproteins (VLDL) is not markedly perturbed by a 0.5% agarose matrix, and variations in mobility primarily reflect differences in particle valence and density of surface charge. Application of electrokinetic theory to derive protein and lipoprotein net charges from the electrophoretic mobilities in agarose yields a quantitative delineation of lipoprotein electrophoretic migration patterns wherein the beta mobility region comprises a surface potential range of -4.5 to -7.0 mV; the pre-beta region a range of -7.0 to -10.5 mV; the alpha mobility region a range of -10.5 to -12.5 mV and the serum albumin region a range of -12.5 to -14.0 mV. Because protein conformation and charge are critical in metabolic regulation, the agarose gel electrophoresis technique provides a valuable analytical tool that should help to elucidate further details of the structure-function relationships of serum lipoprotein particles.