Abstract

The localisation of alkaline phosphatase in human large intestine was investigated at the ultrastructural level. Alkaline phosphatase was found in the mature absorptive cells of the surface, upper, and middle crypt epithelium; the reaction product was localised in the glycocalyx coat of the microvilli, the Golgi apparatus, and the rough endoplasmic reticulum. Slight activity was found in the immature absorptive cells of the middle and lower regions of the crypts. The undifferentiated cells and the enterochromaffin cells were negative. In the lamina propria, alkaline phosphatase was localised in the plasma membrane of the endothelial cells of the venules, in the rough endoplasmic reticulum of the plasma cells, and the cell membrane of macrophages. These results are consistent with the role of alkaline phosphatase in membrane transport.