MUC5AC, BUT NOT MUC2, IS A PROMINENT MUCIN IN RESPIRATORY SECRETIONS

Airway mucus was collected from healthy and chronic bronchitic subject s. The chronic bronchitic sputum was separated into gel and sol phase by centrifugation and mucins were isolated using isopycnic density-gra dient centrifugation in CsCl. The presence of the MUC5AC and MUC2 muci ns was investigated with antisera raised against synthetic peptides wi th sequences from the respective apoproteins. The gel and sol phase of chronic bronchitic sputum as well as healthy respiratory secretions w ere shown to contain MUC5AC whereas the MUC2 mucin could not be detect ed. Rate-zonal centrifugation showed that the MUC5AC mucin was large, polydisperse in size and that reduction yielded subunits. Ion-exchange HPLC revealed the presence of two subunit populations in all secretio ns, the MUC5AC subunits always being the more acidic. MUC5AC is thus t he first large, subunit-based, gel-forming respiratory mucin identifie d and this glycoprotein is biochemically distinct from at least one ot her population of large, gel-forming mucins also composed of subunits but lacking a genetic identity.