Anti‐V region framework antibodies affect the ligand binding of V_L dimer

The effect of antibodies to the light chain variable region (V_L) of protein MOPC‐315 (a, Λ₂), on the binding of hapten by V_L315 dimer or Fv315 (V_L + V_H) was studied by equilibrium dialysis. Anti‐V_L did not change the binding properties of Fv but affected the binding properties of V_L dimer. At pH 5, the binding properties of V_L in the presence or absence of anti‐V_L were the same, whereas at pH 8, anti‐V_L reduced the number of ligands bound to V_L from two to one. It has previously been shown that V_Ldimer binds one ligand at pH 5 and two ligands at pH 8, and that V_L conformation at pH 5 is tighter. Hence, our results suggest that anti‐V_L tightens the conformation of V_L dimer at pH 8.0 such that it can bind only one ligend. Since Fv is not affected by anti‐V_L, the results indicate that a combining site made of two identical chains (V_Ldimer) can undergo a conformational change upon interaction with its antibody. Such conformational change can indirectly affect the binding properties.