Studies on the Active Center of Trypsin

The effectiveness of benzamidine and phenylguanidine as competitive inhibitors of trypsin has been attributed to the binding of their aromatic rings in a hydrophobic slit between the anionic and catalytic sites at the active center of trypsin (1). The normal function of this region of the active center was considered to be the binding of substrate methylene groups in lysyl and arginyl residues. To test this interpretation of the orientation of bound benzamidine and phenylguanidine, derivatives containing ester groups in the para position were prepared and examined for substrate behavior. Esters whose length approximated the extended form of normal substrates were found to be cleaved with kinetic characteristics consistent with this picture.