Plasminogen-binding lipoprotein: isolation and characterization of a plasma very low density lipoprotein which co-chromatographs with plasminogen on lysine-sepharose

By lysine-Sepharose chromatography, approximately 20% of normal plasma samples yield epsilon-aminocaproic acid (EACA) eluates which are opalescent, rather than clear, suggesting the presence of an additional, non-plasminogen component. This material has been isolated and characterized as a plasma lipoprotein of the very low density (VLDL) class on the basis of density ( less than 1.006 g/ml), size (greater than or equal to 5 X 10(7) daltons by gel filtration), electrophoretic mobility (pre-beta), chemical composition (mean cholesterol:triglyceride protein ratio, 1:3.4:1) and immunochemical evidence for apoproteins B, C, and E. Uniform particles, 100-200 Angstroms in diameter, were seen by electron microscopy. In contrast with VLDL in general, this lipoprotein co-chromatographed with plasminogen on lysine-Sepharose, where its binding was plasminogen-dependent, and from which it was eluted by EACA, but at lower concentrations than was plasminogen, suggesting a lysine-binding process. This plasminogen-binding lipoprotein (PBLP) was found in both male and female plasma samples, and increased post-prandially. Its properties suggest that it is a unique subclass of plasma VLDL. Although its isolation explains a laboratory phenomenon, and it exhibits interesting interactions with an important plasma zymogen, its function remains to be determined.