- Complexes of tissue-type plasminogen activator and its serpin inhibitor plasminogen-activator inhibitor type 1 are internalized by means of the low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor. Orth, K., Madison, E.L., Gething, M.J., Sambrook, J.F., Herz, J. Proc. Natl. Acad. Sci. U.S.A. (1992)