Phosphatase(redirected from Placental Alkaline Phosphatase)
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any of the enzymes of the hydrolase class that catalyze the hydrolysis of phosphoric acid esters in animals, plants, and microorganisms. Phosphatases maintain the phosphate level necessary for various biochemical processes; it may be that they also transport phosphate to the cell.
Depending on the chemical nature of the substrate, phosphatases are divided into monophosphatases, for example, glucose 6-phosphatase, which hydrolyze monoesters of phosphoric acid, and diphosphatases, such as nucleases, which break down the diesters of phosphoric acid. Monophosphatases, in turn, are classified as either specific (interacting with only one substrate) or nonspecific (having a wide range of activity). Depending on the nature of the medium in which their maximum activity is observed, nonspecific monophosphatases are referred to as either alkaline (optimal activity at pH 8–10) or acid (pH 4–6). Alkaline phosphatases are found in animal tissue (intestinal mucosa, placenta, kidneys, bones) and in milk, bacteria, and fungi; acid phosphatases are present in the tissue of the prostate gland, spleen, and liver and in yeasts, bacteria, and higher plants.
The most comprehensive studies have been carried out on the structure and mechanism of activity of the alkaline phosphatase in Escherichia coli. The enzyme is composed of two identical sub-units that function alternately; it contains firmly bonded Zn atoms and has a molecular weight of 80,000. The arrangement of the polypeptide chains is known, and it has been established that the reaction with the substrate passes through a stage of enzyme phosphorylation. A determination of the activity of acid and alkaline phosphatases is important in diagnosing diseases, such as rickets, that are accompanied by an increase in phosphatase activity.
REFERENCESThe Enzymes, 3rd ed., vol. 4. New York-London, 1971.
S. M. AVAEVA