Studies on human secretory IgA. II. Comparative studies on a fragment of secretory component derived from secretory IgA and fragments obtained by enzymatic digestion of free secretory component
Kobayashi, K.; Vaerman, J.P.; Heremans, J.F.
Immunochemistry 10(2): 73-80
Reduced and alkylated secretory IgA (SIgA) from human milk released a fragment resembling the secretory component (SC) but having a smaller mol. wt. (34 000-45 000), while also lacking certain antigenic determinants of SC. Reductive cleavage did not affect the mol. wt. or antigenic specificity of free SC (FSC) present in milk. However, enzymatic digestion of FSC by various proteases released fragments which closely resembled the above described fragment from bound SC with respect to mol. wt., antigenic specificity and electrophoretic mobility. Trypsin, chymotrypsin and subtilisin were all found to be very effective in producing these changes, whereas pepsin was less efficient. Compared to FSC, the SC bound to SIgA was resistant to the attack by chymotrypsin. All the SC fragments studied, whether obtained by proteolysis of FSC or by reduction of whole SIgA, showed marked multi-banded electrophoretic polymorphism.