Ornitho-kininogen and ornitho-kinin: isolation, characterization and chemical structure

Ornitho-kininogen was purified from chicken and duck blood plasmas by a two-stage method using chromatography on columns of S-alkylated papain-Cellulofine and DEAE-5PW. The isolated preparation from chicken plasma gave a single band on SDS-PAGE with or without 2-mercaptoethanol and on disc-PAGE. The molecular weight of ornitho-kininogen was estimated as 74,000 on SDS-PAGE using the Ferguson plot method. Ornitho-kininogen was found to have the similar properties to those of mammalian high molecular weight kininogen (HMWK), in terms of the amino acid composition, molecular weight, and susceptibility to plasma kallikrein. No kininogen corresponding to mammalian low molecular weight kininogen (LMWK) and rat T-kininogen could be detected in chicken plasma. In fact, ornitho-kininogen was degraded rapidly by bovine plasma kallikrein, liberating a kinin. This kinin was isolated from the digest by reversed-phase HPLC. The primary structure of the isolated kinin was determined as Arg-Pro-Pro-Gly-Phe-Thr-Pro-Leu-Arg. The sequence of this peptide, named ornitho-kinin, was similar to that of bradykinin except for the substitution of Thr-6 and Leu-8 for Ser-6 and Phe-8. The isolated ornitho-kinin induced a contraction of chicken smooth muscle and had a strong hypotensive effect in the chicken. However, it did not contract the isolated rat uterus. It is suggested that this specificity difference is due to the replacement of Phe-8 by Leu-8. The sequence of residues 1-30 of ornitho-kininogen exhibited 43% identity with that of bovine kininogen.