E myeloma protein, PS, was reduced in different concentrations of dithiothreitol (DTT) for 1 hr followed by alkylation with 14C iodoacetamide. The affinity of the reduced alkylated molecules for target cells was evaluated by their ability to sensitize primate skin in a reversed P K reaction, to sensitize human basophils in a reversed type histamine release and to block passive sensitization with reaginic antibody. Antibody ε0 antibody was employed for reversed type reactions to avoid participation of cell bound normal IgE in the reactions. The sensitizing activity of IgE did not change following reduction in 1 mM DTT, which split inter heavy light chain disulfide bond. The activity of IgE significantly diminished after reduction in 2 mM DTT followed by alkylation. This treatment resulted in the cleavage of 2 intra ε chain disulfide bonds, which are present between the hinge and the Fd portion of the molecules. The reduced alkylated protein was capable of sensitizing primate skin and human basophils, however, a much higher concentration of the reduced alkylated protein than the native protein was required for passive sensitization. The optimal sensitization period for the reversed P K reaction was 3 hr with the reduced alkylated protein. The protein had the ability to block passive sensitization with reaginic antibody. The reduced alkylated protein and the native protein were labeled with 125I, and binding of these proteins with human basophils was examined by autoradiography. The results showed that affinity of the reduced alkylated protein for basophils was less than that of native protein. Since the disulfide bonds split by 2 mM DTT were not included in the Fc portion of the molecule, the Fc fragment was obtained from the reduced alkylated protein and was tested for affinity for basophils. It was found that the Fc fragment had higher affinity than the reduced alkylated protein. Recovery of the affinity by papain digestion strongly suggested that cleavage of disulfide bonds in the Fab portion of the molecules induced conformational changes in the Fc portion which is involved in binding to the target cells. Reduction of IgE with 10 mM DTT followed by alkylation resulted in cleavage of 5 disulfide bonds, which is accompanied by a loss of both sensitizing and blocking activities. The fifth disulfide bond which was cleaved by 10 mM DTT, but not by 2 mM DTT, appears to be an inter heavy chain disulfide bond in the Fc portion of the ε chains. Neither ε1 nor ε2 determinants in the Fc portion of ε chains were degraded by this treatment.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Immunology|
|State||Published - Dec 1 1975|
ASJC Scopus subject areas
- Immunology and Allergy