Immunolocalization of the 33 kD protein in the microvilli of rabbit small-intestinal epithelial cells.

Rabbit small-intestinal microvilli isolated by a Ca2+ precipitation method contain a 33 kD protein, which has not been observed in microvilli isolated in the presence of Ca2+-chelators. The intracellular localization of this protein in rabbit intestinal epithelial cells was studied by immunofluorescence and immunoperoxidase microscopy, and was compared with that of aminopeptidase M, a well-known microvillus membrane-bound enzyme. The results obtained show that the 33 kD protein is located in the inside of the microvillus, but not in the terminal web of the epithelial cell. The protein may also be located on the basolateral surface of the cell.