The membrane attack complex of complement and its precursor proteins lack phospholipase activity

The membrane attack complex of human complement and its highly purified precursor proteins have been analyzed for phospholipase activity. Using three different sensitive assays, phospholipase a₁, A₂, C or D activity could not be detected. Based on the sensitivity of the assays employed, these results indicate the complement-mediated membrane damage is not enhanced by covalent breakdown of membrane phospholipids, but is entirely caused by physical action of the membrane attack complex. The results also imply that the putative serine esterase sites of C6 and C7 are not acting on phospholipids.