Summary
The plasmin substrate, H-D-norleucyl-hexahydrotyrosyl lysine-p-nitroanilide (Spectrozyme-PL),
was found to be equiva lent to 6-aminohexanoate as an enhancer of porcine and human
plasminogen activation by urokinase and of removal of the 1-77 peptide of plasminogen
by plasmin. Activation of plasminogen lacking kringles 1-4, on the other hand, was
not influenced by Spectrozyme PL. Although the rate of activation of human plasminogen
and the modification of human plasminogen by plasmin are faster by an order of magnitude
than that of the activation and modification of porcine plasminogen, both reactions
in the human zymogen, the hydrolysis at arg561-val562 and at lys77lys78, are accelerated by Spectrozyme PL. The findings indicate that kinetic interpretation
of plasminogen activation in solutions containing substrates, where the substrate
has been incorporated to inhibit feedback proteolysis by plasmin, must account for
the cofactor activity as well as the inhibitory activity of the substrate.
