1] Immunoglobulin G (IgG)

Abstract

Publisher Summary This chapter provides an overview of immunoglobulin G (IgG). IgG molecules consist of identical pairs of heavy (H) and light (L) chains (MW = 50,000 and 25,000, respectively) linked by disulfide bridges. A proteolytic enzyme (papain) splits IgG into three fragments which retain biological activity: two Fab (for antigen binding) fragments and one Fc (for crystallizable). Each Fab fragment contains one antigen combining site and consists of one L chain and the amino terminal half of the H chain, termed the Fd fragment. The remaining carboxy-terminal halves of the two H chains, including the inter-H chain disulfide bonds (or hinge region), comprise the Fc fragment which contains the sites responsible for the mediation of most biological functions. Pepsin cleaves IgG at the carboxyl end of the hinge region and thus liberates a bivalent fragment comparable to two papain-derived Fabs, termed F (ab') 2 , as well as a smaller Fc fragment, termed pFc', which contains the C H 3 domain. In most species, immunological memory resides primarily in the IgG antibody response, with certain antigens eliciting preferential responses of one or another of the subclasses. In addition, the chapter also explains purification of immunoglobulin G (IgG).