Purification and characterization of cell growth factor in bovine colostrum

Bovine colostrum has growth factor activity for stimulating DNA synthesis in calf kidney epithelial cells (CKT-1), Madincanine kidney epithelial cells (MDCK) and rat L6 myoblasts (L6), of which the DNA stimulation level and the activity change with the time elapsed after the birth of a calf varied with their respective cells. The growth factor activity of colostrum for CKT-1 was stable regardless of the collection time of colostrum, and it was purified about 3,650-fold in an overall yield of 1.2% from colostrum obtained 30 min after the birth of a calf. The purified growth factor had a molecular weight (MW) of 5,000 and an isoelectric point of pH 9.7, and the amino acid composition was: Asx5, Thr2, Ser4, Glx14, Pro2, Gly4, Ala4, Val2, Ile, Leu2, Tyr, Phe, Lys, His and Arg. The stimulated DNA synthesis in CKT-1 and L6 by the addition of purified growth factor at a final concentration of 16ng/ml was as the same extent as calf serum at a final concentration of 1.52 mg/ml, and the relative activity for CKT-1 was even greater than that for L6.