Isolation of a prokaryotic plasmin receptor. Relationship to a plasminogen activator produced by the same micro-organism.

Plasminogen receptors have been identified on the surface of a number of prokaryotic and eukaryotic cells. A receptor demonstrating high affinity for plasmin with minimal reactivity with the native zymogen Glu-plasminogen has been identified on the surface of certain group A streptococci. In this study the group A streptococcal plasmin receptor has been solubilized and purified to homogeneity. The isolated protein was an Mr approximately 41,000 molecule which retained its ability to bind plasmin following solubilization and affinity purification on a column of enzymatically inactivated human plasmin. The isolated plasmin receptor was compared functionally, antigenically, and physicochemically to the secreted plasminogen activator, streptokinase, produced by the same organism. The Mr approximately 41,000 surface plasmin receptor was shown to be functionally and antigenically distinct from the Mr approximately 48,000 streptokinase molecule produced by the same strain and lacked any plasminogen activator activity. The streptokinase molecule produced by this strain was shown to be closely related to the plasminogen activator protein secreted by other group A and C streptococci. This study represents the first report of the isolation of a plasmin receptor, either prokaryotic or eukaryotic, with functional activity.