Purification of protein A, an outer membrane component missing in Escherichia coli K-12 ompA mutants

Outer membrane materials prepared from an Escherichia coli ompA (tolG) strain do not contain one of the major outer membrane proteins found in ompA+ strains. This protein has been purified in high yield from detergent-solubilized cell envelope material prepared from an ompA+ strain by preparative electrophoresis in polyacrylamide gels containing sodium dodecyl sulfate. The purified protein is homogeneous in three electrophoretic systems, contains 2 mol of reducing sugar/mol of peptide and has alanine as the N-terminal amino acid. The amino acid composition is nearly identical to outer membrane protein II or B purified by others from incompletely solubilized cell envelope material. Thus, the fraction of outer membrane protein II or B that is difficult to solubilize is identical with the more readily solubilized fraction.