Cell adhesion and spreading factor. Partial purification and properties

The fetal calf serum (FCS) factor required for both the specific adhesion and spreading of baby hamster kidney (BHK) cells has been purified 140-fold. The purified factor is a mixture which appears to contain two active globular glycoprotein components. The larger has a sedimentation coefficient of 12.5S and contains polypeptide chains of about 215 000 D and the smaller is 9S and contains popypeptide chains of 94 000, 80 000 and 71 000 D. The mixed factor has been determined to have an isoelectric point of 4.0 and its amino acid and carbohydrate composition have been determined. The low isoelectric point may be a result of the high content of glutamic and asparatic acid (up to 21%) and sialic acid (2-3%). Activity of the mixed factor requires its adsorption onto the substratum surface and about 0.6-0.85 μg of adsorbed factor protein on a 9.6 cm² surface is required for complete cell adhesion and spreading to subsequently occur. Non-specific cell adhesion (i.e., direct adsorption of cells onto the substratum in the absence of serum) can be completely blocked by pre-coating the substratum with bovine serum albumin (BSA); the purified factor can be shown to compete with BSA for the limited number of potential adsorption sites on the substratum surface. The mixed factor adsorbs preferentially to the substratum in the presence of a high excess of BSA and promotes increased cell adhesion and spreading as the density of the factor on the substratum is increased. Experiments with anti-factor antiserum indicated that the mixed factor preparation contains all of the FCS components involved in promoting cell adhesion and spreading.