Abstract
Fragment X, one of several fragments released from bovine plasma high-molecular-weight (HMW) kininogen by the action of bovine plasma kallikrein, was isolated and characterized. The amino acid composition of fragment X was identical with that of a previously characterized glycopeptide, fragment 1•2. However, it had no carbohydrate components. Fragment X was further cleaved by plasma kallikrein into two peptide fragments, named fragment Y and the previously characterized fragment 2. The NH2-terminal sequences up to 15 residues of fragment X and fragment Y were identical with that of fragment 1•2. Further, peptide maps of the tryptic digests of fragment 1•2 and fragment X were indistinguishable, except for the spots corresponding to glycopeptides, which were only found in the digest of fragment 1•2. These results show fragment X to be a carbohydrate-free fragment 1•2, which is a precursor peptide composed of fragment Y and fragment 2. The present studies also provide further evidence for microheterogeneity of the fragment 1•2 region in bovine HMW kininogen, in addition to the previously reported microheterogeneity with amino acid substitutions caused by genetic variants in the same region.
Fragment X, the carbohydrate-free fragment 1•2, showed strong inhibitory activity upon the kaolin-mediated activation of Hageman factor (factor XII), as does hexadimethrine bromide. It also prolonged the calcium-clotting time of citrated rat plasma. These results indicate that fragment X has activities similar to those of fragment 1•2, which has recently been identified as one of the contact activation inhibitors. The oligosaccharide chains attached to the peptide chain in fragment 1•2 are not essential to the inhibitory activity.
