Affinity purification of tissue plasminogen activator using transition-state analogues

The search for a simple affinity ligand to purify tissue plasminogen activator (tPA) was facilitated by a solid-phase synthesis approach. A large variety of tripeptide ligands containing argininal were synthesized on agarose gels containing a spacer with carboxy terminal. The immobilized ligands were easy to test with urokinase, and tPA. While a number of sequence combinations showed initial binding by tPA, only a few resulted in tight binding corresponding to a hemiacetal linkage with the active site serine. Hydrophobic residues, especially aromatics, flanking the N-side of argininal gave rise to ligands which were bound strongly by tPA. A gel containing D-Phe-D-Phe-Argal (an aldehyde derivative of arginine) was very effective in purifying tPA derived from cell culture media at small scale (milligrams) and at large (multi-grams).