The phosphotransferase activity of phosphatases. 2. Studies with purified alkaline phosphomonoesterases and some substrate-specific phosphatases

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Abstract
Alkaline phosphatases from calf intestinal mucosa and from cows milk catalyze synthesis of phosphate esters by direct transfer of the phosphate group from phosphomonoesters to suitable hydroxy compounds. There is no requirement for inorganic phosphate. Kinetic studies of the transfer reaction were carried out with glucose, fructose and glycerol as phosphate acceptors. The products were estimated enzymically. Over the range pH 8 to 10, the rate of synthesis of glucose phosphate varied with pH, but the percentage transfer was independent of pH. The rate of synthesis of new ester and of hydrolysis of the donor varied with the nature and concentration of the donor, but the percentage transfer was independent. Whereas the rate of hydrolysis of the donor decreases, the rate of synthesis of new ester, and of percentage transfer, increases with acceptor concentration up to a limiting value which varies with each acceptor. Neither the initial rate of synthesis of new ester nor the percentage transfer is related to the free energy of hydrolysis of the donor, but both vary considerably with the nature of the acceptor. Kidney hexose diphosphatase, 5[image]-nucleo-tidase and myosin-adenosine triphosphatase failed to catalyze transfer to acceptors other than water. Competition between water and other hydroxyl-containing compounds for sites at the surface of the enzyme-donor complex is postulated to explain the reactions of the alkaline phosphomonoesterases.