HEPARIN INHIBITS ENHANCING FACTOR PHOSPHOLIPASE A(2) ACTIVITY AND ITSBINDING TO THE CELL-SURFACE

Enhancing factor (EF), a mouse intestinal phospholipase A(2) (PLA(2)), has been isolated and characterized, EF increases the binding of epid ermal growth factor (EGF) to A431 cells almost two-fold by interacting with EGF. EF binds to a 100 kDa cell surface receptor and brings abou t an increase in the binding of EGF. In the present study we demonstra te that EF is a heparin binding protein and at the time of iodination of EF, the heparin binding site of EF has to be protected. Heparin inh ibits the enhancing activity of EF as well as the binding of labelled EF to A431 cells. Inhibition of binding of EF to cells by heparin indi cates that heparin binding region forms at least part of the receptor binding domain. These data suggest that the receptor for EF on the cel l surface could be a heparin sulphate proteoglycan.