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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.
Insights
Human immunoglobulin M J chain was purified and analyzed. The J chain exists as dimers in solution, held together by non-covalent forces, with a molecular weight around 29,000.
Area of Science:
- Immunology
- Protein Chemistry
Background:
- Immunoglobulin M (IgM) is a crucial antibody in the innate immune system.
- The J chain is a component of polymeric immunoglobulins, including IgM.
Purpose of the Study:
- To isolate and characterize the J chain from human immunoglobulin M.
- To determine the molecular weight and quaternary structure of the J chain.
Main Methods:
- Electrophoresis on polyacrylamide gels (SDS-PAGE)
- Ultracentrifugation
- Chemical denaturation using guanidine hydrochloride
Main Results:
- Purified J chain exhibited a molecular weight of approximately 27,000 Da by SDS-PAGE.
- Ultracentrifugation in borate-saline solution indicated an average molecular weight of about 29,000 Da.
- Exposure to guanidine hydrochloride led to dissociation into smaller units (approx. 15,000 Da), suggesting dimer formation via non-covalent bonds.
Conclusions:
- Human J chain exists as dimers in solution, stabilized by strong non-covalent interactions.
- The J chain's structure is sensitive to denaturing conditions, revealing its subunit composition.