Polypeptides of a glycoprotein antigen (SF) present in serum and surface of normal but not of transformed chicken fibroblasts.

A protein immunologically identical to a glycoprotein antigen from fibroblast plasma membrane (SF antigen complex) is present in chicken serum. This antigen disappears from cells transformed with tumor viruses. The antigen solubilized from fibroblasts using urea and detergents, and the serum component both gave a molecular weight of about 2-10(5) as estimated by gel filtration on Sepharose 4B. Ultracentrifugation in 5-20% sucrose gradients gave a value of 7-8 S for the antigen from both sources. Isolation of antigen from serum and fibroblasts extracts was achieved using immunochemical techniques. Analysis of the polypeptide chains of the cellular antigen by electrophoresis in the presence of sodium dodecylsulphate, disclosed three major components at molecular weights 210 000 and 145 000 and 45 000. The two high molecular weight bands were identified in electrophoretograms of whole cell extracts by absorption to and subsequent elution from immunoadsorbents. The 45 000-molecular weight components comigrated with purified actin in electrophoresis. After short pulses of (35S) methionine the high molecular weight polypeptides, the 145 000-molecular weight component in particular, were among the most prominent radioactive bands from whole cell extracts indicating that SF antigen has a rapid turn-over. The antigen isolated from serum showed a polypeptide composition similar to the one from cells except the 45 000-molecular weight component was not detectable.