INTERACTION OF THE 2 COMPONENTS OF LEUKOCIDIN FROM STAPHYLOCOCCUS-AUREUS WITH HUMAN POLYMORPHONUCLEAR LEUKOCYTE MEMBRANES - SEQUENTIAL BINDING AND SUBSEQUENT ACTIVATION

The sequential interaction between the two components S and F of leuko cidin from Staphylococcus aureus and the membrane of human polymorphon uclear neutrophils has been investigated in the presence of 1 mM Ca2With I-125-labeled components, it has been shown that binding of the F component occurred only after binding of the S component. The kinetic constants of binding of both components were not statistically differ ent (K-d, approximately 5 nM; B-m, approximately 35,000 molecules per cell), and both Hill coefficients were 1. The application of increasin g concentrations of leukocidin provoked a dose-dependent secretion of the granule content, as determined by hexosaminidase and lysozyme acti vity measurements. Furthermore, the separate perfusion of S and F comp onents on human polymorphonuclear neutrophils deposited on a filter in duced secretion of the granules content only when the perfusion of the S component preceded that of the F component. We conclude, therefore, that (i) S-component binding is a prerequisite for F-component bindin g and for subsequent activation of polymorphonuclear neutrophils and ( ii) there is a specific binding site for the S component in the plasma membrane.