Disulfide-bound proteolytic fragments of gastric mucin are 100-and 140-kDaproteins

Pig gastric mucus was tested for its autodegradative proteolytic degradatio n at pH 7.0, in the presence or absence of proteinase inhibitors and SDS. S amples of crude mucus were incubated at room temperature for 48 and 96 h in sodium azide stabilized buffer, pH 7.0, and urea-extracted mucin was purif ied. Electrophoretically homogenic mucin preparation was reduced and alkyla ted with iodo[C-14]acetamide, and analyzed for labeled products. On 7.5% SD S/PAGE protein bands at 80 and 120 kDa were noted, but radioactivity was in corporated into 100- and 140-kDa bands, with increasing intensity from T-0 to T-96, and into high molecular mass mucin subunits. The results confirmed the autodegradative properties of gastric mucin and demonstrated that the 100- and 140-kDa fragments are the main proteolytical products of pig gastr ic mucin and are disulfide bound with the rest of the molecule. (C) 2000 Ac ademic Press.