title: Cell surface receptor for hemopexin in human leukemia HL60 cells. Specific binding, affinity labeling, and fate of heme.
abstract: The binding of 125I-labeled human hemopexin to human leukemia HL60 cell at 4 degrees C was saturable with time and with increasing concentrations of 125I-hemopexin. Scatchard analysis of the binding data revealed the presence of approximately 42,000 binding sites/cell with an apparent dissociation constant (Kd) of 1.0 X 10(-9) M. When cells were incubated with radioactive hemopexin at 37 degrees C, 125I-hemopexin was rapidly bound and then was dissociated after the release of heme. Treatment of surface-bound 125I-hemopexin with divalent lysine-directed cross-linking disuccinimidyl suberate revealed a membrane polypeptide of about 80,000 Da, to which hemopexin is cross-linked. To examine the fate of the internalized heme, lysates from the cells previously incubated with [59Fe]heme-hemopexin complex were analyzed by CM-cellulose and Sephacryl S-200 column chromatography. A considerable amount of the radioactivity was present in the fraction which co-eluted with the myeloperoxidase activity. When myeloperoxidase was isolated from the cells incubated with [59Fe]heme-hemopexin complex by immunoprecipitation with anti-myeloperoxidase antibody, radiolabeled iron associated with myeloperoxidase increased with time, and more than 30% of the radioactivity in the cells was present in the myeloperoxidase. These results indicate that the binding of hemopexin to the surface receptors triggers a release of heme and that this heme is incorporated into the intracellular myeloperoxidase.
mesh_terms: D000345:Affinity Labels; D001665:Binding Sites; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D006418:Heme / Q000378:metabolism; D006466:Hemopexin / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D007951:Leukemia, Myeloid / Q000378:metabolism*; D008970:Molecular Weight; D009195:Peroxidase / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018000:Receptors, Peptide
chemical_list: D000345:Affinity Labels; D011956:Receptors, Cell Surface; D018000:Receptors, Peptide; C047453:hemopexin receptor; D006418:Heme; D006466:Hemopexin; D009195:Peroxidase