title: Interaction and complex-formation between the eosinophil cationic protein and alpha 2-macroglobulin.
abstract: The interaction between the highly basic and cytotoxic eosinophil cationic protein (ECP) and human plasma proteins is described. The major plasma protein responsible for complex-formation with ECP was shown to be the 'fast' form of alpha 2-macroglobulin (alpha 2M). Large amounts of complexes were observed in a serum obtained from a patient with hypereosinophilic syndrome. The amount of complexes that could be generated in vitro in normal fresh serum was rather low and was even less in fresh citrated plasma. Complex-formation between the non-proteolytic ECP and alpha 2M was augmented in the presence of methylamine. Binding of ECP to alpha 2M was also induced by the proteinases cathepsin G and thrombin, and the binding was competitive with cathepsin G. Methylamine and the proteinases seem to share a common mechanism in inducing binding of ECP. The nature of the ECP-alpha 2M interaction is non-covalent, but withstands high salt concentrations. The interaction with alpha 2M may reflect a mechanism by which the organism protects itself against the deleterious effects of the highly cytotoxic protein ECP.
mesh_terms: D001798:Blood Proteins / Q000378:metabolism*; D056649:Cathepsin G; D002403:Cathepsins / Q000494:pharmacology; D002850:Chromatography, Gel; D047091:Eosinophil Granule Proteins; D006801:Humans; D007122:Immunoelectrophoresis; D046911:Macromolecular Substances; D008744:Methylamines / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D012260:Ribonucleases; D012697:Serine Endopeptidases; D013917:Thrombin / Q000494:pharmacology; D000511:alpha-Macroglobulins / Q000378:metabolism*
chemical_list: D001798:Blood Proteins; D047091:Eosinophil Granule Proteins; D046911:Macromolecular Substances; D008744:Methylamines; D000511:alpha-Macroglobulins; C027451:methylamine; D012260:Ribonucleases; D002403:Cathepsins; D012697:Serine Endopeptidases; C534094:CTSG protein, human; D056649:Cathepsin G; D013917:Thrombin