Chick or bovine transferrin induces proliferation of chick embryo cells cultured in the presence of horse serum, which cannot itself assure their multiplication. Cell growth can also be induced by iron salts and iron complexes such as hemoglobin or hemin, but also by biliverdin which has no iron atom in its molecule.
A new spectrofluorometric method for heme quantitation in cultured fibroblasts is described. The method includes: 1) heme extraction by methanol/sulfuric acid, 2) partial purification of heme by a microchromatographic method, and 3) treatment of the purified heme by oxalic acid followed by fluorometric quantitation. Using this method, heme concentration was determined in chick embryo fibroblasts cultured in a medium supplemented with either 7% fetal bovine serum (FBS) or 10% horse serum (HS). In the presence of FBS, cultured cells actively divided and cells contained 34-55 pmol heme/mg protein. In contrast, cultures maintained in HS proliferated at a slower rate and contained 23-25 pmol heme/mg protein. The addition of 40 microM FeSO4 to cultures maintained in the presence of HS stimulated cell proliferation, and the cellular heme concentration increased to 37-51 pmol/mg protein. These findings suggest that the cessation of growth in the presence of HS may be due to decreased heme content in the cells and that the stimulation of cell growth by iron is mediated by its stimulation of heme synthesis.
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