<prompt> Antigen binding site on antibody is -Hinge regionConstant regionVariable regionHypervariable region  <response>: The antigen combining site of the immunoglobulin molecule is at its amino terminus. - it is composed of both L and H chains. - the first 110 amino acid from the N terminal is quite variable in amino acid sequence and this region is called the variable region: Variable light chain and variable heavy chain. Reference: Anathanarayan paniker;s 9th edition, pg no: 94 p 