PHOSPHORYLATION OF HUMAN PLASMINOGEN ACTIVATORS AND PLASMINOGEN

Plasminogen (PG), urokinase-type plasminogen activator (u-PA) and tiss ue-type PA (t-PA) are the main molecules involved in fibrinolysis and in many other physiological and pathological processes. In the present study we report that human t-PA, purified from human melanoma cells, and PG, purified from human plasma, both contain P-Tyr residues, as re vealed by immunoblotting analyses with monoclonal anti-P-Tyr antibodie s. In addition HPLC amino acid analysis of acid-hydrolyzed t-PA, PG an d u-PA, shows that: (i) P-Ser and P-Tyr residues are present in t-PA; (ii) P-Thr and P-Tyr are present in PG; (iii) P-Ser, P-Thr and P-Tyr a re present in u-PA. The utilization of monoclonal anti-P-Ser and anti- P-Thr antibodies in immunoblotting experiments has confirmed these dat a which indicate that phosphorylation is a common feature of PAs and o f PG.