Primary Structure of Porcine Plasminogen

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Abstract
The single polypeptide chain of native porcine plasminogen (MW .apprx. 90,000) after CNBr-cleavage and gel filtration (Sephadex G-75) yielded a high MW core fraction of fragments linked by disulfide bridges and 3 fragments of lower MW (N-terminal and C-terminal CNBr-fragments and dodecapeptide). From the reduced and S-carboxamidomethylated core fraction an additional 7 fragments with MW between 2000-38,000 were obtained. The CNBr-fragments were aligned in the porcine plasminogen polypeptide chain according to sequence homologies with the known primary structure of human plasminogen. Due to the lack of 2 methionine residues in kringle 1 and in the N-terminal part of the L chain region and to an additional methionine residue in kringle 2, the CNBr-fragment pattern differs from that of human plasminogen. Affinity chromatography of elastase-digested, native plasminogen yielded 3 fragments with intact lysine binding sites, originating from the H chain region and a non-adsorbable fragment, corresponding to human mini-plasminogen. This fragment was converted by urokinase into a proteolytically active protein which served for the isolation of the porcine plasmin L chain. With the aid of the fragments produced by the CNBr and elastase cleavage .apprx. 350 residues were sequenced, of which .apprx. 80% showed identity with the sequence of human plasminogen. This percentage varied depending on the region of the molecule, with the highest extent of identity (80-90%) found in the analyzed kringles 2 and 4.