Membrane Proteins of Escherichia coli K-12: Two-Dimensional Polyacrylamide Gel Electrophoresis of Inner and Outer Membranes

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Abstract
Protein compositions of the inner and outer membranes of E. coli K-12 were analyzed by 2-dimensional gel electrophoresis in which proteins are separated according to apparent isoelectric point (1st dimension) and to apparent MW (2nd dimension). Membrane proteins except for a pair of major outer membrane proteins (proteins Ia and Ib) were solubilized effectively by lysis buffer containing urea, Triton X-100, ampholines and 2-mercaptoethanol. The latter 2 proteins could be solubilized after precipitation of membrane fraction with trichloroacetic acid; they formed a pair of spots at an acidic region on the electropherogram. Another major protein of the outer membrane, protein II*, was also identified. Most of the inner and outer membrane proteins focused at a pH range between 4-6.5. Specific protein patterns characteristic for the inner and outer membranes could thus be visualized by the present system. At least 120 and 50 protein species were detected for the inner and outer membranes, respectively.