Characteristics of complement-dependent release of phospholipid from Escherichia coli

The release of (32)P-labeled bacterial phospholipid from a smooth Escherichia coli by serum components depends on complement activated by antibody. Phospholipid release in excess antibody tends to be proportional to the concentration of complement as does the release of other cellular constituents. Phospholipids are not simply stripped off during cell lysis. Whereas 94% of the total phospholipid freed from E. coli by mechanical lysis sediments at centrifugal forces sufficient to sediment molecules of 10(6) molecular weight, similar centrifugation sediments only 50% of the phospholipid released by antibody-complement. In fact, after mechanical lysis more than 50% of the phospholipid sediments at velocities sufficient to bring down cell envelopes. Although the bulk of the bacterial phospholipid is located in the cell envelopes, isolated (32)P-labeled cell envelopes and phenol-extracted lipopolysaccharide fails to release phospholipids in the presence of antibody-complement. Moreover, ethylenediaminetetraacetic acid, which like antibody-complement causes loss of cellular selective permeability and prepares E. coli cell walls for the action of lysozyme, releases only small amounts of phospholipid from E. coli and these are sedimentable. The most likely mechanism of phospholipid release caused by antibody-complement appears to be the activation directly or indirectly of an enzyme which is present only in the intact cells.