Incubation of His 6 -proHNP1 with CG did not generate mature HNP1 but instead a digestion product that eluted from C18 HPLC later than HNP1 (Fig. 5A ) and had a mass of 3685.4 A.M.U. This mass corresponds to HNP1 with a dipeptidyl (Asn-Met-) aminoterminal extension, consistent with Lys62QAsn63 cleavage by CG (Fig. 5D ). The CG liberated HNP1 product eluted as a single peak (Fig. 5A) , which was resolved into two species by high resolution RP-HPLC (Alliance analytical HPLC system; Fig. 5B ). Peptide in the second peak corresponded to the mass of Asn-Met-HNP-1 (3685. 