Studies on the molecular weight distributions of two mucins.

by negative contrast has shown lipid micelles that might be associated with mucin threads and which disappear after delipidation (Slayter et al., 1984). In rat small-intestinal mucins, different varieties of lipids aie bound to the different parts, naked or hyperglycosylated, of these mucins (Witas et al., 1983). At the present time, there is no published indication of such differences in human bronchial mucins. However, the amount of lipids bound to high molecular weight mucins prepared without reducing agents (Woodward et ul., 1982) is more important than the quantity of lipids bound to mucin prepared after reduction of bronchial secretion, which have a lower molecular weight and a lower content of dicarboxylic acid (Lhermitte et af . , 1977) (Table 1). This indirectly suggests that lipid binds preferentially to the wcalled naked region. Finally, the idea of the naked region being on the same peptide as the higher glycosylated region has to be questioned. High molecular weight mucin preparations still contain some small molecular weight proteins, which are bound to mucin via non-covalent and probably hydrophobic linkages (Rose et al., 1979). One may wonder to which extent these peptides may account for the so-called ‘naked regions’. In conclusion human bronchial mucins from chronic hypersecretion may be viewed as complexes made of long, heterogeneous glycoprotein threads, which may be associated with lipid and hydrophobic peptides.