Streptokinase is a protein produced by certain strains of hemolytic group
C streptococcus, and it was the first clinically useful fibrinolytic. Unlike other
plasminogen activators, streptokinase is not an enzyme and cannot break any bonds in a
plasminogen molecule by itself. It forms an equimolecular compound with plasminogen,
thus forming a streptokinase–plasminogen complex. In the plasminogenic region of the
resulting complex, certain conformational changes lead to a break in a few peptide bonds,
and transformation of this complex into a streptokinase–plasmin complex, or free plasmin,
which also decomposes fibrin.
