Phosphoryl group, transfer alkaline phosphatase

Phosphates of pharmaceutical interest are often monoesters (Sect. 9.3), and the enzymes that are able to hydrolyze them include alkaline and acid phosphatases. Alkaline phosphatase (alkaline phosphomonoesterase, EC 3.1.3.1) is a nonspecific esterase of phosphoric monoesters with an optimal pH for catalysis of ca. 8 [140], In the presence of a phosphate acceptor such as 2-aminoethanol, the enzyme also catalyzes a transphosphorylation reaction involving transfer of the phosphoryl group to the alcohol. Alkaline phosphatase is bound extracellularly to membranes and is widely distributed, in particular in the pancreas, liver, bile, placenta, and osteoplasts. Its specific functions in mammals remain poorly understood, but it seems to play an important role in modulation by osteoplasts of bone mineralization. 

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 third example is a phosphoryl transfer enzyme, alkaline phosphatase. The active site of alkaline phosphatase contains two Zn + ions, with a separation of 3.9 A. One zinc center is used to bind the phosphate monoester substrate, the other to activate Ser-102 for nucleophilic attack on the phosphate group of the substrate via an associative mechanism, as shown... 

The use of a chiral [160,170,180]phosphoryl group to study the steric course of phosphoryl transfer reactions was developed mainly in two laboratories, initially in Knowles group and more recently in Lowe s group. The key step in Knowles approach is the reaction catalyzed by K coli alkaline phosphatase. This... 

In some kinases, such as nucleoside diphosphate kinase, " an intermediate step is the phosphoryl transfer to a group belonging to the enzyme, as happens in ATPase and as was discussed in detail for alkaline phosphatase (Section V.B). In other kinases the phosphoryl transfer occurs directly from the donor to the acceptor in a ternary complex of the enzyme with the two substrates.Often metal ions like magnesium or manganese are needed. These ions interact with the terminal oxygen of the ATP molecule, thus facilitating the nucleophilic attack by the acceptor. The metal ion is often associated with the enzyme. For mechanistic schemes, see the proposed mechanism of action of alkaline phosphatase, especially when a phosphoryl enzyme intermediate is involved. 

Earlier, we have reviewed the most fundamental properties about zincdD s nucleophilicity and the basicity of L— Zn —OH (L = model ligands such as macrocyclic polyamines or tris(pyrazolyl)borate) (6). More recent model studies by us and other groups have been trying to answer further questions (i) Why (or how) is serine needed in alkaline phosphatase More indirectly, what are the points of the serine OH group intervening as acyl- or phosphoryl-transfer agents (ii) Why is a bimetallic system favorable for phosphate hydrolysis (iii) Why does nature adopt zinc(II) as a Lewis acid in zinc enzymes or imidazole as a Lewis base (in the serine-imidazole-carboxylate triad) in serine enzymes (iv) Why are four zinc(II)-bound cysteines used for demethyl-ation (repair) of methyl-DNA phosphotriester, damaged DNA In this review, we want to present the latest results related to these puzzles. 

Given the fact that alkaline phosphatase will catalyze the stereospecific (retention) transfer of a chiral [ 0, 0, 0]phosphoryl group from any monoester to the primary hydroxyl group of 1,2-propanediol (Jones et al., 1978), this method of configurational analysis for chiral monosters can be considered general. 

Fig. 18. Hydrolysis of thymidine 5 -(4-nitrophenyl ( 0, OJphosphate) catalyzed by staphylococcal nuclease (A) and the subsequent transfer of the chiral phosphoryl group to (5)-1,2-propanediol catalyzed by alkaline phosphatase (B). From Mehdi and Gerlt (1982). Copyright 1982 American Chemical Society.

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