Alkaline phosphatase isozymes: recent progress

The past few years have witnessed the reports of significant new events in alkaline phosphatase (AP) isozymes. The cloning of the relevant genes and their nucleotide sequencing have all been accomplished. As a group, the genes for the intestinal, germ cell and placental isozymes have considerable sequence similarity; it is noteworthy that they occupy vicinal positions on chromosome 2, while the tissue unspecific AP gene is located on chromosome 1. The latter makes evolutionary lineage and instances of coordinate expression understandable. Another new development is the demonstration of a phosphatidyl inositol glycan tail on the C-terminus of these chromosome-2 AP genes. This is the major membrane insertion mechanism for AP, which is a cell surface membrane enzyme. This information may be helpful in understanding the phenomenon of the depletion of intestinal mucosal AP during fat absorption. Finally, a discussion has been focussed on recent studies on seminoma and AP, including immunodetection and immunoradiotherapy.