| Abstract: | The binding of labeled hyaluronate to the surface of Simian virus 40-transformed 3T3 cells was studied as a function of 1) pH, 2) ionic strength, 3) temperature, and 4) molecular weight of the hyaluronate. Binding occurred over a wide range of pH values with optima at pH 7 and at less than pH 4. Binding at low pH was eliminated at high ionic strength whereas that at physiological pH was enhanced, with a maximum at 0.5 M NaCl. The enhancement of binding at pH 7 was reversible and independent of the particular salt used. Scatchard plot analysis showed that increasing the ionic strength resulted in both a decrease in the dissociation constant (Kd) and an increase in the amount bound at saturation (Bmax). Temperature also influenced the binding of hyaluronate to the cell surface. The amount bound at low temperatures (0 degrees C) was 3 to 5 times that bound at high temperatures (40 degrees C) with a sharp transition occurring at 18 degrees C, the temperature of phase transition of the plasma membrane. The temperature effect was primarily a change in the Bmax and was reversible. Finally the molecular weight of the ligand influenced the binding. High molecular weight preparations of hyaluronate had a higher binding affinity (lower Kd) and a lower Bmax than did smaller molecular weight preparations. |
