The immunoglobulins can be divided into five different classes, based on differences in the amino acid sequences in the constant region of the heavy chains.

The genetic variations or differences in the constant region determine the three-dimensional structure of the molecule. All immunoglobulins within a given class contain similar heavy chains.

The classes of immunoglobulins can de divided into subclasses based on small differences in the amino acid sequences of constant regions in heavy chains.

All immunoglobulins within a subclass have similar amino acid sequences in the constant regions of heavy chains. In placental mammals e.g. man there are nine classes that migrate in five different groups in electrophoresis; each one consist of two light and two heavy protein chains, and each group has distinguishing structural and functional properties.

ADVERTISEMENTS:

They are known as IgA (a-alpha), IgD (8 – delta), IgE (e – epsilon), IgG (y – gamma) and IgM (jj – mu). Immunoglobulin class switching can be used to change the class of the heavy chain, but not of the light chain.