ABSTRACT
A lack of information on the biochemical details of the type, location, and regulation of proteolytic enzymes decreased the significance of many experiments and prevented the establishment of definite relationships. The best studied of the cellular proteolytic systems involved in cell migration and tissue degradation is the activation of plasminogen. A malignant cell can detach from the original tumor mass, migrate, and establish itself in a distant organ where it can reproduce a tumor with properties similar to those of the one from which it originates. The resulting active enzyme plasmin consists of two polypeptide chains held together by disulfide bonds. The light chain contains the active site that has homologies with trypsin, chymotrypsin, and elastase. Plasmin is an active serine protease which has a relatively broad trypsin-like specificity, hydrolyzing proteins and peptides at lysyl- and arginyl- bonds. Plasmin is rapidly inhibited by alpha-2 antiplasmin, and at a much higher concentration by alpha-2 macroglobulin, both occurring in plasma.
