CELLULAR AND SUBCELLULAR-LOCALIZATION ALONG THE DIGESTIVE AND PULMONARY TRACTS OF A RABBIT INTESTINAL MUCIN DIFFERING FROM MUC2 AND CONTAINING A 150-KDA LIGHT-CHAIN

Two immunologically different rabbit intestinal mucins were separated by performing fractionated ammonium sulfate precipitation, dialysis ag ainst pH 5,5 buffer and filtration through a Sepharose CL 2B column. T hey each contain a light chain with apparent molecular masses of 150 a nd 140 kDa, respectively: These L-chains were purified after reduction and carboxymethylation of the disulfide bridges of the native mucins, and their first 22 amino acid sequence was determined. The sequence o f the 140 kDa chain is 100 % and 95 % identical to the N-terminal sequ ence of the L-chains from human and rat MUC2, respectively and only 54 % identical to the sequence of the 150 kDa chain, It can be concluded that the rabbit counterpart of MUC2 exists and that another rabbit int estinal mucin, named here M-6G2, contains an L-chain. As in the case o f MUC2, the M-6G2 L-chain may have resulted from a limited proteolysis , This proteolysis seems to occur in a region which is conserved in bo th mucins, since the two chains both have approximately the same lengt h and the same five-amino acid N-terminal sequence, The cellular expre ssion of M-6G2 along the digestive and respiratory tracts differs from that of the other mucins known so far to be present in the human smal l intestine.