Protein blotting through a detergent layer, a simple method for detecting integral membrane proteins separated by SDS-polyacrylamide gel electrophoresis.

To selectively detect amphiphilic proteins from a mixture of proteins separated by SDS-polyacrylamide gel electrophoresis, the gel was electro-blotted through another polyacrylamide gel containing a non-ionic detergent (NP40) onto a nylon membrane filter. Most soluble proteins of E. coli passed through the detergent-containing gel, whereas a major fraction of the proteins from the cytoplasmic (inner) membrane, including the lactose and melibiose carrier proteins, were trapped in the detergent layer. The major outer membrane proteins, OmpA, OmpF and LamB, partitioned to the detergent layer only when solubilized at low temperature which avoids complete denaturation. This simple procedure, termed "detergent blotting", should have wide application in the study of integral membrane proteins.