No abstract

No abstract

The cloning of mucin cDNAs brought about by the application of molecular biology and molecular analyses constitutes a major step in understanding mucin structure and function. Here two classes of mucins are described: epithelium-associated and endothelium/leukocyte-associated mucins, which have thus far been described separately in the literature. The epithelial mucins are generally believed to play a role in cytoprotection. The endothelial and leukocyte class of mucins are adhesion molecules involved in lymphocyte homing and lymphocyte activation or are part of the adhesion cascade that plays a role in the initiation of inflammation. Mucins in general contain many threonine and serine residues, which are extensively O-glycosylated. Due to this profound glycosylation, mucins have a filamentous conformation. By virtue of their extended filamentous, and often negatively charged, structure, mucins can act as a barrier protecting the cell. However, when an opposing cell has specific receptors for mucins, adhesion can override the barrier function. Therefore, mucins may be powerful two-edged swords: they are both protective and adhesive.

No abstract

The hydrolytic enzymes of the intestinal brush border membrane are essential for the degradation of nutrients to absorbable units. Particularly, the brush border glycohydrolases are responsible for the degradation of di- and oligosaccharides into monosaccharides, and are thus crucial for the energy-intake of humans and other mammals. This review will critically discuss all that is known in the literature about intestinal brush border glycohydrolases. First, we will assess the importance of these enzymes in degradation of dietary carbohydrates. Then, we will closely examine the relevant features of the intestinal epithelium which harbors these glycohydrolases. Each of the glycohydrolytic brush border enzymes will be reviewed with respect to structure, biosynthesis, substrate specificity, hydrolytic mechanism, gene regulation and developmental expression. Finally, intestinal disorders will be discussed that affect the expression of the brush border glycohydrolases. The clinical consequences of these enzyme deficiency disorders will be discussed. Concomitantly, these disorders may provide us with important details regarding the functions and gene expression of these enzymes under specific (pathogenic) circumstances.