The portion of an immunoglobulin's heavy and light chains having an amino acid sequence that does not vary within a given class or subclass of immunoglobulin.
The portion of an immunoglobulin molecule's heavy and light chains that determines the class or subclass of the immunoglobulin and that is almost identical in amino acid sequence in all molecules of a particular class or subclass.
The portion of the amino acid sequence of an antibody's heavy or light chains that determines the class of the antibody and does not vary within a given class. The constant region terminates in a free carboxyl group (COOH). Unlike the variable region, the constant region does not interact with antigens.