Fig 8-1. The N-terminal end of IgGl is characterized by sequence variability(V) in both the heavy and light chains, referred to as the VH and Vi regions respectively. The rest of the molecule has a relatively constant(C) structure. The constant portion of the light chain is armed the Cl region. The constant portion of the heavy chain is further divided into three structurally discrete regions: Chl, CH2 and ch3. These globular regions, which are stabilized by intrachain disulphide bonds, are referred to as 'domains'. The sites at which the antibody binds antigen are located in the variable domains. The hinge region is a segment of heavy chain between the CHI and CH2 domains. Flexibility in this area permits the two antigen-binding sites to operate independently. There is close pairing of the domains except in the Ch2 region. Carbohydrate moieties are attached to the Ch2 domains. 免疫球蛋白在血清自由电泳图谱中主要分布在r一球蛋白区域,因此以前有人把r一球 蛋白误认为就是抗体。其实r一球蛋白不全是抗体,而抗体也不全在r一球蛋白区域内(见 图8-2)。 8-2人血清免疫球蛋白的分布 Distribution of the major human immunoglobulins albumin electrophoretic mobility Fig8-2 Electrophoresis of human serum showing the distribution of the four major immunoglobulin classes. Serum proteins are separated according to their charges in an electric field, and classified as al, a2, B and y, depending on their mobility(lge class has a similar mobility to lgd but cannot be represented quantitatively because of its low level in serum). lgg exhibits most charge heterogeneity, the other classes having a more restricted mobility in theβ and fa8156 Fig 8-1. The N-terminal end of IgG1 is characterized by sequence variability(V) in both the heavy and light chains, referred to as the VH and VL regions respectively. The rest of the molecule has a relatively constant(C) structure. The constant portion of the light chain is termed the CL region. The constant portion of the heavy chain is further divided into three structurally discrete regions: CH1, CH2 and CH3. These globular regions, which are stabilized by intrachain disulphide bonds, are referred to as ‘domains’. The sites at which the antibody binds antigen are located in the variable domains. The hinge region is a segment of heavy chain between the CH1 and CH2 domains. Flexibility in this area permits the two antigen-binding sites to operate independently. There is close pairing of the domains except in the CH2 region. Carbohydrate moieties are attached to the CH2 domains. 免疫球蛋白在血清自由电泳图谱中主要分布在г－球蛋白区域，因此以前有人把г－球 蛋白误认为就是抗体。其实г－球蛋白不全是抗体，而抗体也不全在г－球蛋白区域内（见 图 8-2）。 图 8-2 人血清免疫球蛋白的分布 Fig8-2 Electrophoresis of human serum showing the distribution of the four major immunoglobulin classes. Serum proteins are separated according to their charges in an electric field, and classified as 1,   and   depending on their mobility. (IgE class has a similar mobility to IgD but cannot be represented quantitatively because of its low level in serum). IgG exhibits most charge heterogeneity, the other classes having a more restricted mobility in the  and fa8