Serum-free conditioned medium from human lung obtained at autopsy provides a rich source of colony stimulating factor which stimulates granulocytic and macrophagic colony growth in both mouse and human bone marrow. The appearance of the factor is enhanced by endotoxin and inhibited by either puromycin or actinomycin D. Human lung colony stimulating factor is stable at the pH range of 6.5-10 and temperature of 56°C for 30 min. It is resistant to trypsin and neuraminidase but is sensitive to subtilisin, chymotrypsin and periodate. It shows heterogeneity on Sephadex gel filtration with two activity peaks having molecular weight of 200 000 and 40 000, respectively. Upon gel electrophoresis, human lung colony stimulating factor migrates in the α-globulin post-albumin region. Using the combination procedures of hydroxyapatite chromatography and preparative polyacrylamide gel electrophoresis a 600-fold purification was achieved with a final specific activity of 6 · 105 units per mg protein. The purified colony stimulating factor is very labile: however, the activity can be stabilized by the addition of gelatin or bovine serum albumin at the concentration of 0.1% and 0.2 mg/ml, respectively.
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