Bovine plasma HMW and LMW kininogens. Structural differences between heavy and light chains derived from the kinin-free proteins.:Structural Differences between Heavy and Light Chains Derived from the Kinin-free Proteins

Kinin-free proteins which were produced by the incubation of high-molecular-weight (HMW) kininogen with plasma kallikrein [EC 3.4.21.8] and of low-molecular-weight (LMW) kinino-gen with snake venom kininogenase were prepared. Each of the isolated proteins yielded two polypeptide chains, named heavy and light chains, after cleavage of their disulfide bridges. The heavy chains derived from the two kinin-free proteins were found to have almost the same molecular weight of 48, 000. However, the molecular weights of their light chains differed markedly; that of the HMW-light chain was 16, 000 and that of the LMW-light chain was 4, 800. These heavy and light chains were located in the amino and carboxyl terminal portions of the parent molecules and were held together by a single disulfide bridge, as judged from their terminal residues and amino acid compositions.<br> As regards the overall amino acid compositions and terminal residues, the heavy chains from the two kinin-free proteins were very similar, and they cross-reacted immunologically with an antibody against the heavy chain isolated from kinin-free HMW protein. Further, tryptic peptide mappings of the two heavy chains supported their structural similarity. How-ever, there was a slight difference in carbohydrate content; HMW-heavy chain contained 12.6%, whereas LMW-heavy chain contained 19.3%. On the other hand, the light chains derived from the two kinin-free proteins showed clear differences not only in molecular weight but also in their chemical properties, including amino acid and carbohydrate compositions, terminal residues and N-terminal sequences.<br> These results indicate that the major structural difference between HMW and LMW kininogens exists in the large C-terminal portions following the bradykinin moieties along the polypeptide chains. Based on the gross molecular structures of HMW and LMW kininogens, their possible functional roles are discussed.