The immunoglobulin having highest molecular weight is:

Ans. B. Ig MImmunoglobulins, a specialized group of proteins are mostly associated with gamma globulin fraction (on electrophoresis) of plasma proteins. All the Ig molecules consist of two identical heavy (H) chains and two identical (L) chains. Each have constant and variable regions. Humans have five classes of Ig- IgG, IgA, IgM, IgD and IgE. Out of these IgM is the largest composed of 5-Y shaped units held together by a J polypeptide chain. Due to its largest size, IgM cannot traverse blood vessels, hence it is restricted to the blood stream.