constant region

constant region n the part of the polypeptide chain of a light or heavy chain of an antibody that ends in a free carboxyl group -COOH and that is relatively constant in its sequence of amino acid residues from one antibody to another called also constant domain compare VARIABLE REGION

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the C-terminal portion of an immunoglobulin heavy chain (C_H) or light chain (C_L), comprising one homology region in light chains and three or four in heavy chains; it has a constant amino acid sequence for chains of a single type produced by one individual. Constant regions vary among the heavy chain classes and subclasses (isotypic variation) and among individuals (allotypic variation). Called also C r. See illustration at immunoglobulin.