Expression of alkaline phosphatase loci in mammalian tissues

Publisher Website
Google Scholar
Abstract
Alkaline phosphatases (EC 3.1.3.1) were examined in liver, bone, kidney, intestine and placenta from 9 mammalian species [pig, cat, dog, hamster, cow, sheep, guinea pig, mouse and rat] by quantitative inhibition and thermostability studies and compared with alkaline phosphatases in the corresponding human tissues. In humans, 3 kinds of alkaline phosphatase can be sharply differentiated by these methods, 1 occurring in liver, bone and kidney, 1 in intestine, and 1 in placenta. They are evidently determined by separate gene loci. In the mammals only 2 sorts of alkaline phosphatase were found: 1, which occurs in liver, bone, kidney and also placenta, corresponds to the human liver/bone/kidney enzyme and the other corresponds to the human intestinal enzyme. The findings support the earlier proposal that the expression of a distinctive type of alkaline phosphatase in human placenta is the consequence of a late evolutionary event which occurred subsequent to the divergence of the evolutionary lineage leading to humans from the various lineages leading to other mammalian species. The concentrations of the inhibitors, phenylalanine, homoarginine, phenylalanylglycylglycine and levamisole, required to give 50% inhibition, [I50], of the liver/bone/kidney/placental (nonhuman) alkaline phosphatases showed no significant variation among the species. The [I50] values for the intestinal enzyme varied among species to a much greater extent. This implies that in the liver/bone/kidney/placental (nonhuman) alkaline phosphatase the structures of the binding sites for these inhibitors, were highly conserved during mammalian evolution, but there was much greater divergence of these structures in the evolution of intestinal alkaline phosphatases.