Streptokinase binds to lactate dehydrogenase subunit-M, which shares an epitope with plasminogen

The bacterial thrombolytic agent streptokinase binds to human, porcine, and chicken lactate dehydrogenase (EC 1.1.1.27; LD) isoenzyme subunit M, but not to the H or C subunits. There is amino acid sequence homology between LD and the streptokinase binding site on plasminogen to account for this interaction that results in the formation of high-molecular-mass complexes in serum that contain LD activity. Binding of highly immunogenic streptokinase with LD may lead to induction of anti-LD autoantibodies, known to occur in some patients after therapeutic administration of streptokinase for treatment of acute myocardial infarction. This interaction may also be a general mechanism for inducing autoimmunity against other proteins that share the streptokinase binding epitope.