Abstract
Despite of accumulated information of the LBS (lysine binding site) of the plasmin, little is known of characteristic stereogeometry at the active center. The present studies were kinetically made by using selective synthetic substrates or inhibitors, with expectations that tri-pod structure of highly selective substrates and inhibitors would indicate the replica structure of the active center. From the results obtained, we conclude that the plasmin active center assumes the following three pockts; (1) the first pocket is characterized just to fit the positively charged head of the lysine residue, (2) the second is equipped with very fine structure just to fit (2R, 4R) structure of 4-metyle-2-piperidine-carboxylic acid, but not other stereoisomers of the above mentioned radical (Table 1), and (3) when examined by D-Ile-L-Phe-L-Lys-pNA, 3-methyl-valeric acid-L-Phe-L-Lys-pNA and L-Ile-L-Phe-L-Lys-pNA, the third pocket is to fit (a) D-Ile-, (b) 3-methyl-valeric acid-, and (c) L-Ile-, with differend Km values (a) 20μM, (b) 180μM, and (c) 330μM respectively, the highest affinity of the third pocket for the terminal D-Ile derivative being indicated (Table 2).
