Studies on synthetic peptide substrates for F XII enzymes

Screening of chromogenic peptide substrates have shown that FXIIa readily splits substrates of D-Pro-Phe-Arg-pNA (S-2302) and -Gly-Arg-pNA (e.g. S-2222) types. The latter type is preferred in a system where kallikrein is present. By using the substrate S-2222 a method for the determination of beta FXIIa inhibitors has been designed. Chromatography data show that C1-esterase inhibitor is the major inhibitor of beta FXIIa in plasma. Preliminary studies have also been performed on the assay of FXII in human plasma. The procedure to obtain a complete activation of FXII has still to be studied.