RESUMEN
Marked sensitivity to proteolytic degradation results in the loss of multiple antioxidant properties of ceruloplasmin (CP), the multicopper oxidase of mammalian plasma. In this study, gel filtration of virtually pure CP (purity 99.7%) yielded complexes of this protein. Subjecting the complexes to SDS-free PAGE revealed other proteins along with CP. These were identified as matrix metalloproteinases (MMP-2 and MMP-12) by means of tryptic fragment mass spectrometry. Electrophoretic bands corresponding to MMP-2 (72 and 67 kDa) and MMP-12 (22 kDa) displayed gelatinase activity. The identified proteinases contained heparin-binding motifs inherent in the complex-forming partners of CP, such as lactoferrin, myeloperoxidase, and serprocidines. Therefore, admixtures of MMPs can be efficiently eliminated from CP preparations by chromatography on heparin-Sepharose as proposed previously.