BIOSYNTHESIS OF RAT MUC2 IN COLON AND ITS ANALOGY WITH HUMAN MUC2

In order to identify the mucins synthesized and secreted in the rat co lon, we studied their biochemical characteristics and biosynthesis and evaluated their analogy to human colonic mucins. Purified mucin from both species appeared similar with respect to composition, buoyant den sity and mobility on SDS/PAGE. Isolated rat colonic mucin (RCM) was us ed to elicit a polyclonal antiserum, which was used in metabolic label ling studies to identify mucins and mucin precursors. RCM is synthesiz ed as a 600 kDa precursor protein, which oligomerizes before O-glycosy lation. The mature, high-molecular mass mucin is secreted and displays an anomalous molecular mass on SDS/PAGE of approximately 650 kDa. Pol ymorphism in precursor size was found among different rats, suggesting genetic heterogeneity. Molecular mass, biosynthesis and secretion of RCM appeared similar to human MUC2. Moreover, RCM precursor could be i mmunoprecipitated using specific anti-(human MUC2) antisera, indicatin g that the RCM can be designated rat MUC2. This study describes the bi osynthesis of two homologous mucins in two different species. The high degree of similarity suggests functional analogy.