Tryptic digestion of bovine secretory IgA at elevated temperature and in urea. Isolation of SC domain 1 which is covalently bound to IgA dimer and binds non-covalently to IgM.
1. Tryptic cleavage sites in bovine secretory component (SC) which become inaccessible when SC is bound to IgA dimer remained inaccessible at 60 degrees C and in 4 M urea at 37 degrees C. 2. This suggests the presence of strong interactions compatible with published affinity constants of ca 10(8) M-1. 3. In 5 M urea at 37 degrees C further cleavage of bound SC did occur to produce a fragment consisting of domain 1 which was disulphide bridged to the IgA dimer. 4. Binding studies on the isolated fragment showed that domain 1 did not account for all the binding by SC. 5. Cleavage of the isolated fragment with iodosobenzoic produced a smaller fragment consisting of the n-terminal third of domain 1 (residues 1-35). This N-terminal fragment showed significant binding.
Beale
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Agricultural and Food Research Council, Institute of Animal Physiology and Genetics Research, Babraham, Cambridge, England.
D000478:Alkylation; D000818:Animals; D002417:Cattle; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D006358:Hot Temperature; D007070:Immunoglobulin A / Q000378:metabolism*; D007071:Immunoglobulin A, Secretory / Q000378:metabolism*; D007128:Immunoglobulin Fragments / Q000378:metabolism*; D007075:Immunoglobulin M / Q000378:metabolism*; D007463:Iodobenzoates / Q000494:pharmacology; D010084:Oxidation-Reduction; D012635:Secretory Component / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism*; D014364:Tryptophan / Q000378:metabolism; D014508:Urea
D007070:Immunoglobulin A; D007071:Immunoglobulin A, Secretory; D007128:Immunoglobulin Fragments; D007075:Immunoglobulin M; D007463:Iodobenzoates; D012635:Secretory Component; C008154:2-iodosobenzoic acid; D014364:Tryptophan; D014508:Urea; D014357:Trypsin