Identification of Different Forms of the Murein‐Bound Lipoprotein Found in Isolated Outer Membranes of Escherichia coli

Abstract

The identification of the free and murein-bound forms of the E. coli lipoprotein on dodecylsulfate-polyacrylamide gels was systematically investigated by analyzing the low MW proteins (MW < 20,000) of cytoplasmic and outer membranes. The free form of the lipoprotein was identified on 15% polyacrylamide gels as the fastest migrating component (MW = 7200-7500) of the isolated outer membranes; it could be separated from a small cytoplasmic membrane protein (MW = 6500) which was probably identical to the dicyclohexylcarbodiimide binding proteolipid of the membrane-bound ATPase. Lysozyme treatment of both outer membranes and murein sacculi failed to convert the murein-bound lipoprotein into a fragment of uniform size; instead the bound form appeared as a series of bands consisting of lipoprotein bound to 1, 2, ... 8 murein subunits. The composition of this ladder depended on the method used to isolate outer membranes. Beside these lipoprotein bands the outer membrane contained 2 other proteins, III and V; the relation of these proteins to previously described proteins is discussed.