The subunit and polypeptide-chain structure of rabbit secretory immunoglobulin A. Isolation of a proteolytic fragment suitable for sequence studies on the variable region of α-chain

A method was developed for the preparation of a proteolytic fragment of rabbit secretory immunoglobulin A (sIgA) which contains the variable region of the alpha-chain; this fragment is suitable for primary-sequence studies. The serologically defined subclasses of sIgA are shown to correlate partially with the nature of the binding of a constituent chain of sIgA, called secretory piece. Data are also presented on the relative resistance of sIgA to enzymic and reductive cleavage, compared with immunoglobulin G.