The Intestinal Cell Surface: Some Properties of Normal, Undifferentiated, and Malignant Cells

The isolation of the microvillus and basolateral portions of the intestinal cell has made possible a better understanding of the structure and function of these surface components. The microvillus membranes contain both hydrolytic (for example, disaccharidases, dipeptidases) and synthetic enzymes (such as glycosyltransferases) and possess the carrier proteins involved in sugar and amino acid transport. Membrane vesicles have been used to show the presence of such carriers in the membrane. Most of the adenylate cyclase activity appears to be in the basolateral rather than microvillus membranes. In contrast with villus cells, the undifferentiated, mitotically active crypt cells are not active in transport and have glycoproteins on their cell surface that are incomplete. Furthermore, the surface membranes of crypt cells also have a high activity of the enzyme galactosyltransferase and are agglutinated by the plant lectin, concanavalin A. These surface properties of crypt cells are strikingly similar to fetal and malignant cells.