Summary
A ternary equimolar human plasmin B-chain-streptokinase-plasminogen complex was isolated
from a mixture of the plasmin B-chain-streptokinase complex and human plasminogen
at 0° C and 37° C. A ternary complex which was shown to be species specific, was identified
and characterized by ultracentrifugal, acrylamide gel electrophoretic, and agarose
double diffusion analyses. When mixed at a 1:1 molar ratio at 0° C, 39.9% of the preparation
existed as a plasmin B-chain-streptokinase-plasmino-gen complex; when mixed at 37°
C, 86.d% existed as a complex, which was identified by electrophoretic analyses to
be a plasmin B-chain-streptokinase-plasmin complex. Sedimentation velocity analyses
gave s°2o,w values of 3.79 for the plasmin B-chain-streptokinase complex, 4.10 for Lys-plasmin,
and 6.23 for the plasmin B-chain-streptokinase-plasmin complex. Sedimentation equilibrium
analyses gave molecular weights of 73,900 for the plasmin B-chain-streptokinase complex,
82,900 for Lys-plasmin, and 153,100 for the plasmin B-chain-streptokinase-plasmin
complex. The diisopropylphosphorofluoridatc (DFP)-inhibitcd and the p-nitrophenyl-p-guanidino-benzoate
(NPGB)-inhibited plasmin B-chain-streptokinase complexes both retained their ability
to form a ternary complex with human plasminogen, but this complex did not convert
to a plasmin B-chain-streptokinase-plasmin complex. Thus, the active site serine residue
is essential for the activator activity of the plasmin B-chain-streptokinase complex,
but it is not necessary for the binding of the plasmin B-chain-streptokinase complex
to plasminogen to form a ternary complex.
Keywords
Plasmin B-chain - Streptokinase - Plasminogen - Plasmin B-chain-streptokinase-plasminogen
complex