Final answer:
The antigen binding site of an immunoglobulin is formed from both V regions of the heavy and light chains, which are responsible for the specificity of antigen binding.
Step-by-step explanation:
The antigen binding site of an immunoglobulin is formed from both V regions from the heavy and light chains. Immunoglobulins, or antibodies, have a basic Y-shaped structure composed of two heavy chains and two light chains. The antigen binding site is located at the ends of the Y structure.
Each chain consists of a variable region (V) and a constant region (C), with the variable regions responsible for the diversity and specificity of antigen binding. It is the combination of the variable regions from both the heavy and light chains that come together to form the actual antigen-binding site.
The hypervariable regions, which contribute to the binding specificity, are also called complementarity determining regions (CDRs).