Rat Immunoglobulin purified protein are antibody molecules. Rat IgG is composed of four peptide chains — two heavy chains (gamma) and two light chains. Rat IgG has two antigen binding sites. Other Immunoglobulins may be described in terms of polymers with the IgG structure considered the monomer. Rat IgG typically constitutes 75% of serum immunoglobulins. Rat IgG molecules are synthesized and secreted by plasma B cells.