Abstract
Human secretory IgA is mainly a disulfide‐bonded dimer whose polymer conformation is secondarily stabilized by conjugation with one molecule of “secretory piece” (SP). The noncovalent interactions between SP and IgA are highly dependent upon an apparently variable number of disulfide bridges between the same units, and are responsible for a packing of the composite molecule to a degree that the most immunogenic region of SP is masked. This inaccessible (I) determinant, as well as one of its accessible (A1) antigenic groups, is extremely susceptible to reduction‐alkylation. Antigenically intact SP can therefore hardly be obtained by degradation of secretory IgA. The released molecules are of the same size as native free SP, but a proportion of them may have only one (A2) or two (A2 and A1) unimpaired determinants. Maximum release of SP with three reactive determinants occurs after reduction with 5 mM dithioerythritol, 0.075 M β‐mercaptoethanol, or 0.05–0.075 M cysteine‐HCl—the first two followed by alkylation.
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Schedule a callMore From: Acta Pathologica Microbiologica Scandinavica Section B Microbiology and Immunology
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