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 against pH 5.5 buffer and filtration through a Sepharose CL 2B column. They each contain a light chain with apparent molecular masses of 150 and 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 of the 140 kDa chain is 100% and 95% identical to the N-terminal sequence 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 intestinal mucin, named here M-6G2, contains an L-chain. As in the case of 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 both mucins, since the two chains both have approximately the same length and the same five-amino acid N-terminal sequence. The cellular expression 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 small intestine.