Poly-d-lysine dependent inactivation of tissue plasminogen activator by a class pai-2 inhibitor (minactivin)

Abstract

Two-chain tissue plasminogen activator (t-PA) was found to be inactive in a coupled colorimetric assay for plasminogen activators, but a high level of activity was obtained in the presence of poly-D-lysine. This stimulated activity was strongly inhibited by minactivin, a urokinase inhibitor, but unstimulated enzyme could be shown to be unaffected by minactivin. In the presence of poly-D-lysine minactivin was a very successful competitive inhibitor of t-PA with respect to the substrate, plasminogen. The K i for minactivin determined by the Henderson method was 2.5 × 10 -12 M, compared to the K m for plasminogen determined as 0.6 × 10 -6 M. The value of K i for minactivin with u-PA, determined under the same conditions, was 1.6 × 10 -11 M.