Phosphate alkaline phosphatase and

In a cross-sectional study in 28 adults with epilepsy who took oxcarbazepine monotherapy for 1 year and 28 healthy volunteers, [226 ] although alkaline phosphatase and vitamin D3 concentrations were significantly different, calcium, phosphate, alkaline phosphatase, and bone densitometry were not different from baseline after 1 year. 

In subsequent years, much evidence has been adduced to support this mechanism. Alkaline phosphatase and, by analogy, other serine enzymes, are directly phosphorylated on serine serine phosphate is not an artifact (Kennedy and Koshland, 1957). In the presence of nitrophenyl acetate, chymotrypsin is acetylated on serine, and the resulting acetylchymotrypsin has been isolated (Balls and Aldrich, 1955 Balls and Wood, 1956). Similarly, the action of p-nitrophenyl pivalate gave rise to pivaloyl chymotrypsin, which could be crystallized (Balls et al., 1957). Neurath and workers showed that acetylchymotrypsin is hydrolyzed at pH 5.5, but that it is reversibly denatured by 8 M urea the denatured derivative is inert to hydrolysis and even to hydroxylamine, whereas the renatured protein, obtained by... 

In enzymes, the most common nucleophilic groups that are functional in catalysis are the serine hydroxyl—which occurs in the serine proteases, cholinesterases, esterases, lipases, and alkaline phosphatases—and the cysteine thiol—which occurs in the thiol proteases (papain, ficin, and bromelain), in glyceraldehyde 3-phosphate dehydrogenase, etc. The imidazole of histidine usually functions as an acid-base catalyst and enhances the nucleophilicity of hydroxyl and thiol groups, but it sometimes acts as a nucleophile with the phos-phoryl group in phosphate transfer (Table 2.5). 

Horiuchi et al. (2), and Torriani (S) that orthophosphate repressed the formation of a nonspecific phosphomonoesterase in E. coli that research on this enzyme began. This work (2, 3) showed a maximum rate of synthesis of the enzyme occurred only when the phosphate concentration became low enough to limit cell growth. With sufficient phosphate, the amount of active enzyme is negligible. Under conditions of limiting phosphate, alkaline phosphatase accounts for about 6% of the total protein synthesized by the cell (4). 

As noted earlier, the binding of Mg2+ to ATP results in activation towards hydrolysis of the terminal phosphoryl group. Hydrolysis and transfer of phosphate may involve transfer of the phosphoryl group to the enzyme, followed by transfer to water or an acceptor molecule. Enzymes such as alkaline phosphatase and fructose-1,6-biphosphatase which require Mg2+ and Zn2+ will be considered in Section 62.1.4. 

The transfer of phosphate is stimulated by l,25-(OH)2D3, but little is known about the mechanism. Vitamin D also stimulates the activities of alkaline phosphatase and Ca2+-ATPase. This may be involved in the supply of inorganic phosphate. 

Dixit, P. K. Quantitative histochemistry of cartilage. Alkaline phosphatase and glucose-6-phosphate dehydrogenase activity in different zones of rachitic rat cartilage during healing. Calc. Tiss. Res. JO, 49-57 (1972). 

Reaction mixtures contained in a volume of 0.5 ml 50 jimoles HEPES pH 7.0, 0.5 pmoles CoCI2, 45 hq KOO-8-phosphate phosphatase or 5 / g alkaline phosphatase, and 0.5 mg of the appropriate compound, incubated at 35°C. Data for both enzymes are expressed as specific activities (pmoles per min per mg protein) under the above conditions of incubation. 

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