[150] values for the intestinal enzyme varied among species to a much greater extent. This implies that in the liver/one/ kidney/placental (nonhuman) alkaline phosphatase the structures of the binding sites for these inhibitors have been highly conserved during mammalian evolution, but there has been much greater divergence of these structures in the evolution of intestinal alkaline phosphatases.At least three gene loci determine the various forms of alkaline phosphatase [ALPase; orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1] that occur in human tissues: one coding for the placental form, at least one coding for the intestinal forms (adult and fetal), and at least one coding for the liver, bone, and kidney forms (1-4). These three classes of ALPase are sharply discriminated from one another by quantitative inhibition with L-phenylalanine (Phe), L-homoarginine (Har), and L-phenylalanylglycylglycine (PheGlyGly) as inhibitors and also by their thermostabilities (1,5,6). In a recent study using these criteria we compared the ALPases occurring in liver and in placenta from a series of mammals with those occurring in human liver and placenta (7). We found that in each of the animal species studied the liver and placental ALPases closely resembled each other and were also very similar to human liver ALPase, but they differed from human placental ALPase. We have now extended these studies to include bone, kidney, and intestinal ALPases from the various species. We have also extended the battery of inhibitors to include levamisole, which is a particularly potent inhibitor of liver, bone, and kidney ALPase (8, 9).We find that the liver, bone, kidney, and placental ALPases from the various species resemble each other and also human liver, bone, and kidney ALPases very closely, but they are sharply differentiated from the series of intestinal ALPases and from human placental ALPase. The results suggest that in these mammalian species there are two distinct forms of ALPase, a liver/bone/kidney/placental form and an intestinal form,

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Alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1] in placenta, intestine, liver, kidney, bone, and lung from a variety of primate species has been characterized by quantitative inhibition, thermostability, and immunological studies. Characteristic human placental-type alkaline phosphatase occurs in placentas of great apes (chimpanzee and orangutan) but not in placentas of other primates, including gibbon. It is also present in trace amounts in human lung but not in lung or other tissues of various Old and New World monkeys. However, a distinctive alkaline phosphatase resembling it occurs in substantial amounts in lungs from Old World monkeys but not New World monkeys. It appears that duplication of alkaline phosphatase genes and mutations of genetic elements controlling their tissue expression have occurred relatively recently in mammalian evolution.

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