IMMUNOCHEMICAL ANALYSIS OF THE ERYTHRINA PROTEASE INHIBITOR

Two monoclonal antibodies directed to the Kunitz-type trypsin/tissue p lasminogen activator inhibitor of Erythrina seeds (ETI) were obtained from mice that had been immunized with the native inhibitor. Both anti bodies reacted with the native molecule, as well as with the inhibitor that had been cleaved at its trypsin reactive site, and from which th e reactive site Arg 63 had been removed. The antibodies cross-reacted weakly with a homologous inhibitor derived from winged beans, and with the human plasminogen activator inhibitor I (PAI-1). They did not cro ss-react with the closely related soybean trypsin inhibitor, the lima bean inhibitor, inhibitors in peanut extracts, and ovomucoid. The anti bodies were directed against closely spaced epitopes and were shown to interfere with the inhibition of both trypsin and t-PA by ETI. The fa ct that we could not show that it was directed to the reactive site le ads us to suspect that the inhibitory antibodies exert their effect ei ther by steric hindrance or by distant allosteric reactions rather tha n by direct blockage of the reactive site of the molecule.