ABSTRACT
Enhancing factor (EF), a mouse intestinal phospholipase A2 (PLA2), has been isolated and characterized. EF increases the binding of epidermal growth factor (EGF) to A431 cells almost two-fold by interacting with EGF. EF binds to a 100 kDa cell surface receptor and brings about an increase in the binding of EGF. In the present study we demonstrate 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 inhibits 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 indicates that heparin binding region forms at least part of the receptor binding domain. These data suggest that the receptor for EF on the cell surface could be a heparin sulphate proteoglycan.