A Modified Nonequilibrium pH Gradient Electrophoresis (NEPHGE) Technique for Protein Separation

Abstract

Membrane proteins, hydrophobic proteins, and proteins with alkaline isoelec-tric points (pIs) traditionally have been difficult to visualize by two-dimensional (2-D) gel electrophoresis. There are a multitude of reason as to why proteins with basic pIs (many of them membrane proteins) are difficult to resolve by standard IEF methods: (i) the lack of pH gradient formation above pH 7.6 due to the buffering effect of urea, (ii) precipitation of proteins when entering the gel and during focusing, (iii) cathodic drift during focusing resulting in the migration of basic proteins off the ends of the tube gels, or (iv) lack of solubility in particular nonionic detergents. O’Farrell et al. first reported in 1977 a novel protein separation technique termed Nonequilibrium pH Gradient Electrophoresis (NEPHGE) as a method to enhance the separation of proteins with significantly basic pIs (1), but this alternative technique had its limitations due to issues with reproducibility with the reagents of that era. With the advent of new compounds for the solubili-zation of recalcitrant proteins, my laboratory has made minor modifications to the original NEPHGE protocol reported by O’Farrell offering enhanced reproducibility with increased solubilization of alkaline and membrane proteins (2–4).