Liver endoplasmic reticulum polypeptides resolved by two-dimensional gel electrophoresis

Several modifications of the two-dimensional electrophoretic technique of P. H. O'Farrell (i.e., first-dimensional isoelectric focusing followed by second-dimensional sodium dodecyl sulfate electrophoresis: 1975, J. Biol. Chem. 250, 4007) were required for maximum resolution of rat liver smooth microsomal polypeptides without significant artifact. All substantial changes were in isoelectric focusing which gave ∼55 bands with 130 μg of microsomal protein; subsequent electrophoresis in the second dimension yielded ∼230 polypeptide spots. Mild deoxycholate treatment to lyse microsomes suggested that ∼170 spots represent integral membrane proteins. Comparisons of two-dimensional polypeptide patterns for liver microsomes from phenobarbital-induced, 3-methylcholanthrene-induced, and noninduced rats revealed differences mainly in putative cytochrome P-450 polypeptides.