The molecular weight of J chains derived from human immunoglobulin M

Abstract

J chain was isolated from sulphonated human immunoglobulin M molecules by electrophoresis on polyacrylamide gels. When determined by electrophoresis in sodium dodecyl sulphate-polyacrylamide gels, the molecular weight of the protein was about 27000. After suspension in 5m-guanidine hydrochloride solution for 21 days, two groups of three bands appeared on the gels. Most of the protein dissociated to components of molecular weight 15000. The molecular weight of purified J chain was also determined by ultracentrifugation. In borate-saline solution the average weight-average molecular weight was about 29000. The molecular weight slowly decreased upon prolonged exposure to guanidine hydrochloride, and after 14 days the minimum molecular weight was about 15000. Some association between chains still existed. These data suggest that J chain derived from the paraprotein exists in borate-saline solution as dimers held by strong non-covalent forces.

The incorporation of J chain into reassembled human immunoglobulin M

“…It is known, however, that J chain is attached to IgM molecules through disulphide bridges. Although it was reported that one J chain is associated with one IgM molecule (Mestecky et al, 1972;Morrison & Koshland, 1972), the stoicheiometry is questionable in the light of newer data about the molecular weight of J chain and its tendency for self-association (Kownatzki, 1971;Kobayashi et al, 1973;Ricardo et al, 1974). It is possible that the polymerization of IgMs in vivo requires not only J chain but also an enzyme, not yet identified, which influences disulphide-bond formation.…”