The effect of the carboxy-terminal lysine of urokinase on the catalysis of plasminogen activation.
When single-chain pro-UK is activated by plasmin or kallikrein, the Lys158-Ile159 bond is cleaved, leaving a C-terminal lysine on the A-chain (Lys-UK). Two-chain, high molecular weight urokinase (UK) purified from urine, however, has been shown to contain a phenylalanine residue as the C-terminal of the A-chain (Phe-UK). Since C-terminal lysine residues have a strong binding affinity for plasminogen that may promote its activation, we undertook kinetic studies comparing plasminogen activation by Lys- and Phe-UK. A two-stage method was employed in order to minimize factors known to interfere with plasminogen activation and plasmin determination. The Lys-UK was prepared by plasmin activation of pro-UK purified from human fetal kidney cell culture medium. The Phe-UK was prepared by carboxypeptidase B (CpB) treatment of Lys-UK. Removal of the C-terminal lysine of Lys-UK by CpB produced small but significant increases in the Michaelis constants for the activation of both Glu- and Lys-plasminogen. The apparent Michaelis constants for Glu-plasminogen activation by Lys- and Phe-UK were 3.7 microM +/- .36 microM and 5.9 microM +/- .70 microM, respectively and the Michaelis constants for Lys-plasminogen activation by Lys- and Phe-UK were 5.4 microM +/- .72 microM and 15.2 microM +/- 1.4 microM, respectively. The catalytic efficiency (kcat/Km) of Lys-UK was approximately 2-fold greater than that of Phe-UK for the activation of either Glu- or Lys-plasminogen. When the fibrinolytic activities of Lys- and Phe-UK were compared in a plasma milieu no significant differences were detected. In conclusion, the findings indicate that the C terminal lysine on the A-chain of UK significantly promotes the catalysis of plasminogen in a purified system. However, the higher catalytic efficiency of Lys-UK was not found to induce significant acceleration of clot lysis at pharmacological concentrations in plasma.
Lenich
C
C
Vascular Research Laboratory, New England Deaconess Hospital, Boston, MA.
Pannell
R
R
Gurewich
V
V
D002384:Catalysis; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007700:Kinetics; D008239:Lysine / Q000737:chemistry / Q000378:metabolism*; D010649:Phenylalanine / Q000737:chemistry; D010958:Plasminogen / Q000378:metabolism*; D011392:Proline / Q000737:chemistry; D014568:Urokinase-Type Plasminogen Activator / Q000737:chemistry*
D010649:Phenylalanine; D010958:Plasminogen; D011392:Proline; D014568:Urokinase-Type Plasminogen Activator; D008239:Lysine