Urea gradient/SDS-PAGE; a useful tool in the investigation of signal transducing G proteins

We describe an updated and improved protocol to perform urea gradient/SDS-PAGE in which proteins are electrophoresed through 9% polyacrylamide gel slabs in the presence of a linear 4 M to 8 M gradient of urea using Laemmli's separation buffers. We provide examples of this technique to separate PTX labeled G protein alpha subunits, as well as unlabeled alpha and beta subunits of G proteins. Applications of the technique are exemplified in which (1) the chromatographic separations of G proteins in DEAE-Toyopearl and MonoQ columns are compared, (2) the complexity of PTX substrates expressed in human erythrocytes, bovine brain, dog ventricle, FRTL-5 cells, HIT cells, GH4C1 cells and RIN cells are compared, and (3) the polypeptide composition of G protein beta gamma subunits, as expressed in several tissues and found in three distinct G proteins from a single cell population, are analyzed.