Isolation and purification of a low-molecular-weight skeletal growth factor from human bones

A low-molecular-weight potent bone cell mitogen termed human skeletal growth factor (human SGF) was purified to homogeneity from human bone matrix. Extraction and initial purification steps were done under dissociative conditions to separate human SGF from high-molecular-weight complexes of bone matrix proteins. SGF activity was extracted from human femoral heads by demineralization with 10% EDTA in the presence of 4 M guanidine-HCl and proteinase inhibitors and was purified by hydroxyapatite, HPLC gel-filtration and HPLC reverse-phase chromatography. Human SGF thus purified was homogeneous by HPLC reverse-phase chromatography and SDS-polyacrylamide gel electrophoresis. The relative molecular mass of human SGF purified under dissociative conditions was 11 000. Human SGF stimulated bone cell proliferation ([³H]thymidine incorporation and cell number) at picomolar concentrations, with half maximum activity at 2-3 ng/ml (180-270 pM). Human SGF constitutes 0.00024% of organic bone matrix by weight.