Alkaline phosphatase biological role

Spijkerman, E. and Coesel, P.F.M. (1998) Alkaline phosphatase activity in two planktonic desmid species and the possible role of an extracellular envelope. Ereshwater Biology 39, 503-513. 

Since thionein is usually found in the metal-saturated form Mcy-thionein, the search for its biological function has been focused in the past primarily on roles as a metal repository in cells and tissues exposed to elevated concentrations of Zn ", Cu", Cd ", and others (Webb 1987), or as an in vitro donor of metals (Zn, Cu) to newly synthesized apoforms of metalloenzymes, such as carbonic anhydrase, alkaline phosphatase, and superoxide dismutase (Bremner 1991). However, as biosynthesis provides for a steady supply of the metal-free and metal-seeking apoprotein thionein, it is equally important to view the role of this form as a powerful intracellular acceptor and competitor for metal ions, among them in particular for zinc. In fact, it is chemically most reasonable to consider both Zny-thionein and thionein as conjugates of a zinc donor/zinc acceptor couple whose concentrations fix pZn and thereby regulate the availability of zinc within the cell. Values for the average apparent stability constant, pH 7.o> determined by two independent methods for pH 7.0, are listed in Table 1. 

Whyte, M. P. (2010). Physiological role of alkaline phosphatase explored in hypo-phosphatasia. In Zaidi, M. (ed.) Skeletal Biology and Medicine. Oxford Blackwell Publishing. 

A number of other enzymes which catalyze the hydrolysis of phosphoesters are of biological importance. These include cyclic purine phosphodiesterase (little is known about its active site chemistry at present, but more shall be said about its biological role shortly) and the phosphatases. Acid and alkaline phosphatase catalyze the hydrolysis of phosphomonoesters to the corresponding alcohol and inorganic phosphate. Their pH optimums are 5.0 and 8.0, respectively hence their names. Both form covalent enzyme-substrate intermediates ... 

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