Studies on human kininogens. I. Isolation, characterization, and cleavage by plasma kallikrein of high molecular weight (HMW)-kininogen.

1. Human high molecular weight (HMW)-kininogen was highly purified from human plasma by chromatographies on QAE-Sephadex A-50 and CM-Sephadex C-50. Human HMW-kininogen thus purified was a mixture of a single chain and a disulfide-linked pair of chains. Human HMW-kininogen is an acidic glycoprotein having a molecular weight of 120,000. The amino acid composition of human HMW-kininogen is quite similar to that of bovine HMW-kininogen. 2. We investigated whether the liberation of kinin from human HMW-kininogen by human plasma kallikrein was accompanied by liberation of histidine-rich fragments, as observed with bovine HMW-kininogen (Han et al. (1975) J. Biochem. 77, 55--68). After prolonged incubation of human HMW-kininogen and human plasma kallikrein followed by gel-filtration on Sephadex G-50, a fragment of molecular weight 8,000 was isolated together with bradykinin. However, the histidine content of the fragment was not as high as that in the bovine fragments. Most of the histidine in human HMW-kininogen was recovered in the kinin-free protein, and the light chain of kinin-free protein was found to be rich in histidine compared with the heavy chain. These results suggest that the histidine-rich sequence in human HMW-kininogen is not released by the action of human plasma kallikrein, but remains bound to the light chain of kinin-free protein.