High affinity binding sites on plasma membrane obtained from the lymphoblastoid cultured 1301 cell line for highly radioactive serum thymic factor.

The interaction of the synthetic serum thymic factor (FTS, facteur thymique sérique) with a plasma membrane preparation of human T lymphocytes from the lymphoblastoid T cell line 1301 was studied using 3H-labelled FTS (specific activity 120 Ci/mmol). The binding is temperature dependent and function of the concentration of both 3H-labelled FTS and membrane proteins. At 37 degrees C, using 1 nM of 3H-labelled FTS as steady state is observed within 80 min. The binding is reversible, specific and saturable. Scatchard analysis reveals the existence of at least two binding sites with respective Kd of the order of 0.516 +/- 0.2 nM and 110 +/- 27.8 nM with concentration of 0.186 +/- 0.045 pmol and 2.026 +/- 0.367 pmol per mg of membrane protein.