This glycoprotein is probably not a functional part of the chloride channel. Homodimer; disulfide-linked. Electroplax tissue, brain (200-fold less), and heart (500-fold less). Binds 4-acetamido-4'-isothiocyanostilbene-2,2'-dis ulphonic acid (SITS), an inhibitor of a variety of anion transport proteins. Belongs to the glycosyl hydrolase 31 family. Although related to the glycosyl hydrolase 31 family, lacks the conserved active sites, suggesting it has no glycosidase activity.