. "Protein encoded by a constant region gene (C gene / C segment). The constant region is the region of the immunoglobulin (Ig) that is invariable in its amino acid sequence within any class of immunoglobulin. Each immunoglobulin is a tetramer of two identical light chains and two identical heavy chains linked by disulfide bonds. The light chain has one variable region (VL) and one constant region (CL) domain, whereas the heavy chain has one variable region (VH) and three or four constant region domains (CH1 to CH4). Variable and constant regions are encoded by separated genes, called V genes and C genes respectively, which join during cell differentiation." . . "Immunoglobulin C region" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .