To obviate the difficulties resulting from partial solubility of membrane proteins in detergents or from the use of noxious solvent mixtures containing phenol or chloral, a simple procedure was devised for acrylamide gel electrophoresis of membrane proteins in 13 M formic acid. Polyacrylamide gels are equilibrated in 13 M formic acid and used in the electrophoresis assembly with 13 M formic acid as the electrolyte. Particulate proteinaceous preparations are dissolved in trifluoroacetic acid or in 24 M formic acid containing glycine to increase the density and to facilitate the solubilization of the protein. Protein samples (10 to 100 Kg) migrate as polycations.
Acrylamide gel zone electrophoresis of proteins insoluble in aqueous solutions presents special problems: Chemicals with higher proteinsolvent power may be used as the electrolyte, or protein derivatives with enhanced solubility can be formed for use with ordinary aqueous electrolytes. The latter procedure invariably involves extra manipulations and the possibility of irregular degrees of modification and side reactions.
Sodium dodecyl sulfate, sometimes with reducing agents and urea (l-4) has been useful in solubilizing proteins, including those of membrane origins, and a useful correlation between migration distance and molecular weight exists, but solubilization is often incomplete. The combination of dilute acetic acid as the electrolyte plus solubilization by urea has proved useful for the separation of myelin proteins (5).
By replacing some or all of the water of the electrolyte by more potent protein solvents such as a phenol-acetic acid mixture (6) phenolformic acid mixtures (7), or chloral (8), separations of water-insoluble proteins can be achieved.
The classical techniques of (water-soluble) protein chemistry are nearly useless for separating some membrane proteins. Some separation schemes for myelin proteins involving solvent extraction and nonaqueous chromatographic procedures were devised (9-11). Although it is possible to obtain stable aqueous solutions of some of the membrane