Antigenic markers of V domain of mouse MOPC 21 IgG1 L chain. The conformational basis of VL domain markers and content of MOPC 21 VL‐like immunoglobulins in sera of inbred mouse strains

Antisera were raised in rabbits against L chains, isolated from mouse myeloma protein MOPC21 (γ1,x, Vx15 group). Specific antibodies for the V and C domain of MOPC 21 L chain were obtained by cross‐immunoadsorption of the antisera. The pure anti‐V and anti‐C antibodies were fixed on diazocellulose and used as immunosorbents. The inhibitory capacity of L chain‐monomers and dimers isolated from the L chain preparation was compared to that of intact IgG1 using binding inhibition of 125I‐labeled IgG1 on the antibody‐containing immunosorbents. It was established that changes of IgG1 quaternary structure influences the conformational state of the L chain V domain only. The inhibitory capacity of the V domain is 1000‐fold lower in L monomers, if compared with native IgG1, and only 10‐fold lower than in L dimers. The inhibiting capacity of the C domain, however, does not differ in L monomers and intact IgG1. Thus the conformational rigidity of the C domain co‐exists with conformational flexibility of the V domain on the same polypeptide chain. We tried to estimate the content of MOPC 21 VL‐like normal IgG in mouse serum of 6 inbred strains using antibodies against the VL domain. Data obtained by inhibition of radioimmunoadsorption, indicate that in C57BL/6 mice 0.08% of normal serum Ig carries a VL region which is idiotypically related to the VL of MOPC 21. In serum Ig of BALB/c mice the percentage is 0.16.