Human placental alkaline phosphatase differs from that of other species

Abstract

AT LEAST three gene loci seem to be involved in determining the various forms of human alkaline phosphatase (ALP)—one coding for the placental form of the enzyme, at least one coding for the intestinal forms, and at least one for the liver, bone and kidney forms^1,2. These three classes of human alkaline phosphatase can be distinguished from one another by their behaviour with certain inhibitors, their thermostabilities and their electrophoretic and immunological characteristics. Recent studies have shown that in the dog, the ALP present in placenta closely resembles that in liver, and that these enzymes are very similar to the ALP present in human liver but different from the ALP present in human placenta^3,4. It has also been reported that human placental ALP differs from other mammalian placental ALPs in certain respects (for example, sensitivity to L-phenyl-alanine inhibition)^5,6. In view of these results we have examined some of the characteristics known to distinguish human placental and human liver ALPs, in the liver and placental ALPs from a series of mammalian species. The species from which both tissues were obtained included rodents, carnivores, ungulates and one primate (rhesus). We report here that the properties of human placental ALP differ from those of human liver ALP, whereas in the other species studied, placental and liver ALPs show similar properties.