THE FINDING THAT SECRETORY COMPONENT IS NOT ASSOCIATED WITH γ-GLUTAMYLTRANSPEPTIDASE ACTIVITY

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Abstract
The .gamma.-glutamyltranspeptidase activity of human milk was concentrated by ammonium sulfate precipitation. On gel chromatography of the dissolved precipitate, the activity was eluted in the high MW fraction containing secretory Ig[immunoglobulin]A, while no activity appeared in the eluate at the position of free secretory component. Various antisera were added to portions of the pool of active fractions. No change of .gamma.-glutamyltranspeptidase activity was obtained with antisera against IgA, secretory IgA or secretory component, while a large reduction of activity was seen with anti-human colostrum. Purified free secretory component, secretory IgA and in vitro complexes between secretory component and IgA dimers were inactive in the .gamma.-glutamyltranspeptidase assay, in the absence and presence of Zn ions. Secretory component, when free or bound to IgA, does not exhibit .gamma.-glutamyltranspeptidase activity and cannot function as such an enzyme in the transport of IgA across mucous membranes, as was previously suggested.