Hydrolysis of phosphate monoester

Hydrolysis of phosphate monoester dianions RO-OPOJ [83] Hydrolysis of axial tetrahydropyranyl acetals [79]... 

Converging lines of evidence have led to a general acceptance of the monomeric metaphosphate mechanism for the hydrolysis of phosphate monoester monoanions. The pH rate profile for aryl and alkyl phosphate monoester hydrolyses commonly exhibits a rate maximum near pH 4. where the concentration of the monoanion is at a maximum. The proposed mechanism is based on these principal points of evidence (a) a general observation of P-O bond cleavage (b) the entropies of activation for a series of monoester monoanions are all close to zero, which is consistent with a unimolecular rather than a bi-molecular solvolysis where entropies of activation are usually more negative by 20 eu7 (c) the molar product composition (methyl phosphate inorganic phosphate) arising from the solvolysis of the monoester monoanion in a mixed methanol-water solvent usually approximates the molar ratio of methanol ... 

Recently, theoretical calculations suggested that the rate of HO- attack on the neutral phosphate monoester is very fast.229 Earlier studies underestimated this rate and the present result indicates that the hydrolysis of phosphate monoesters in aqueous solution is not inconsistent with a mechanism that involves proton transfer to the phosphate oxygen followed by nucleophilic attack on the phosphorus. The hydrolysis of... 

J. B. Vincent, M. W. Crowder, B. A. Averil, Hydrolysis of phosphate monoesters a biological problem with multiple chemical solutions, Trends in Biochemical Science 1992, 27, 105-110. 

The electrostatic model for the micellar effect on the hydrolysis of phosphate monoesters is also consistent with the results of inhibition studies (Bunton et al., 1968, 1970). The CTAB catalyzed hydrolysis of the dinitrophenyl phosphate dianions was found to be inhibited by low concentrations of a number of salts (Fig. 9). Simple electrolytes such as sodium chloride, sodium phosphate, and disodium tetraborate had little effect on the micellar catalysis, but salts with bulky organic anions such as sodium p-toluenesulfonate and sodium salts of aryl carboxylic and phosphoric acids dramatically inhibited the micelle catalysis by CTAB. From equation 14 and Fig. 10, the inhibitor constants, K, were calculated (Bunton et al., 1968) and are given in Table 9. The linearity of the plots in Fig. 10 justifies the assumption that the inhibition is competitive and that incorporation of an inhibitor molecule in a micelle prevents incorporation of the substrate (see Section III). Comparison of the value of for phenyl phosphate and the values of K for 2,4-and 2,6-dinitrophenyl phosphates suggests that nitro groups assist the... 

Elimination-addition is a mechanistic pathway open to hydrolysis reactions, for example, when they are performed in a strong base and when the substrate is charged as in Scheme 7.4. A highly unstable intermediate is generated in the rate-determining first step. This mechanism is especially prevalent in the hydrolysis of phosphate monoesters,... 

Cryptate complexes with macrobicychc hgands containing three bipy units, in which the Ln + ion is contained within a hgand cavity, have been synthesized. Such hgands will complex Ln + ions, such as Eu + and Sm +, under conditions where Ln + ions are not. An application has been using lanthanide cryptates of the early lanthanides (La, Ce, Eu) as catalysts in the hydrolysis of phosphate monoesters, diesters, and triesters. Schiff base complexes can be synthesized by the reaction of a lanthanide salt with a diamine and a suitable carbonyl derivative such as 2,6-diacetylpyridine. 

Purple acid phosphatases (PAPs) catalyze the hydrolysis of phosphate monoesters with mildly acidic pH optima (5-7) utilizing a binuclear metal center containing a ferric ion and a divalent metal ion. PAPs are also characterized by their purple color, the result of a tyrosine (Tyr) to Fe3+ charge transfer transition at about 560nm.113 All known mammalian PAPs are monomeric and have a binuclear Fe3+-Fe2+ center, whereas the kidney bean and soybean enzymes are dimeric and have an Fe3 + -Zn2+ center in each subunit. The X-ray structures for kidney bean PAP114 and the PAP115 from rat bone reveal that despite a sequence similarity of only 18%, they share very similar catalytic sites. The structure of the kidney bean PAP shows the two metal ions at a distance of 3.1 A, with a monodentate bridging Asp-164. These and other residues involved in metal coordination can be seen in Fig. 21. 

Taken together, the data indicate direct phosphoryl transfer to a metal-bound water molecule without a phosphoenzyme intermediate. A Bronsted analysis found a value of (j of -0.3 for V/K,137 similar to the value for the uncatalyzed hydrolysis of phosphate monoester monoanions, which could be indicative of charge neutralization on the leaving group in the transition state via protonation. 

Acid phosphatase (EC 3.1.3.2) enzymes catalyze the hydrolysis of phosphate monoesters following the general equation (1). 

On the other hand, phosphorane intermediates are not expected to be involved in the hydrolysis of phosphate monoesters, so the effective observed catalysis by the carboxyl group of salicyl phosphate 3.21 [51] (Scheme 2.26) is presumed to be concerted vith nucleophilic attack. (The hydrolysis reaction involves the less abundant tautomer 3.22 of the dianion 3.21, and the acceleration is >10 -fold relative to the expected rate for the pH-independent hydrolysis of the phosphate monoester dianion of a phenol of pK 8.52.) However, this system differs from the methoxy-methyl acetals discussed above, in that there is a clear distinction between neutral nucleophiles, which react through an extended transition structure similar to 3.16 in Scheme 2.23, and anions, which do not react at a significant rate, presumably because of electrostatic repulsion. This distinction is well-established for the dianions of phosphate monoesters with good leaving groups (p-nitrophenyl [52] and... 

Enzymes that Catalyze the Hydrolysis of Phosphate Monoesters 322... 

Figure 14 General mechanism for hydrolysis of phosphate monoesters catalyzed by PTPs.

Further demonstrations of the effectiveness of particular cations in phosphoryl transfer reactions include the reduced activity of LiF, in contrast to other fluorides, in nucleophilic catalysis and the requirement for two Mg " ions in the enzymic hydrolysis of phosphate monoesters by inositol monophosphatase. ... 

The effectiveness of the binuclear complex 11 (Fig. 13), with two mononuclear cyclen-cobalt(III) units linked together by an anthra-cenyl spacer (cyclen = 1,4,7,10-tetraazacyclododecane), was compared with the monomer in the hydrolysis of phosphate monoesters (354). The reaction assisted by this rigid binuclear complex, having a phosphate-sized pocket, was 10 times faster than that promoted in the presence of two equivalents of the single cyclen-Co complex. In these experiments the substrate concentration was 25 pM and the total cobalt concentration was 2 mM at 25°C and neutral pH (354). No such cooperativity could be noted using a diester substrate because the pseudo-first-order rate constants were similar for both 11 and the mononuclear complex. With 11 as catalyst, an overall rate enhancement of 10 was achieved over the uncatalyzed hydrolysis of paranitrophenyl phosphate monoester as substrate. 

The dissociative mechanism (1) for the hydrolysis of phosphate monoesters was originally invoked to explain the enhanced reactivity of the monoanion-monoacid form of methyl phosphate (Bunton et al., 1958 Butcher and Westheimer, 1955). The facts that were cited in support of the applicability... 

The most potent catalysts for the cleavage of phosphate diesters are octahedral Co(ni) complexes with cis-tetraamine and aquo ligands. These accelerate the hydrolysis of phosphate diesters with much more effect than they accelerate the hydrolysis of phosphate monoesters. Chin and Zou... 

Hydrolysis of phosphate monoesters may proceed by either the associative or dissociative pathway depending on the type of phosphate ester (including the pK values of stepwise deprotonation of the phosphate ester), the properties of the leaving group and the pH of the solution. The neutral diprotonated form of the phosphate monoesters (and other neutral phosphoramidates and polyphosphates) appears to react via the associative pathway, while the mono-and di-anionic forms react solely by the dissociative pathway (Shen and Morgan, 1973 Wijesekera, 1992). 

A later study in a hard-water meso-trophic lake also investigated the separate fate of i C- and P-labelled glucose 6-phosphate into bacterial-sized particles and phytoplankton (Hernandez et al., 1996). Aquatic bacteria and phytoplankton assimilated the phosphoryl moiety 100 times faster than they assimilated the glucosyl moiety. Bacterial uptake conformed to Michaelis-Menten kinetics with an apparent K, of 86 nM and a of 1.4 nM/min. Phytoplankton took up phosphoryl with an apparent K of 380 nM and a V of 7.6 nM/min. These investigators determined the concentration of naturally occurring phosphate monoesters to be between 25 and 40 nM. Comparison of the rate of phosphoryl uptake from glucose 6-phosphate with the phosphate uptake rate indicated that phytoplankton could satisfy a significant portion (42-99%) of their phosphorus demand by hydrolysis of phosphate monoesters. A similar comparison indicated that bacterial assimilation of phosphorus from... 

Determination of ALP ALP catalyzes the hydrolysis of phosphate monoesters such as esters of alcohols, phenols and amines, and inorganic pyrophosphates. ALP occurs in cell membranes throughout most of the tissues of the body. High levels of ALP activity in serum arise from hepatobiliary disease, bone disease, and transient hyperphosphatasemia in children. The value of the y-GT activity is often useful to differentiate, whether an elevation of ALP activity comes from the liver or the bones high levels of both suggest liver origin. ALP has many isoenzymes that are useful for laboratory diagnosis. 

The monometaphosphate anion is believed to be formed initially in the hydrolysis of phosphate monoesters of the type R0P(0)(0H)2, but it is rapidly attacked by nucleophiles and this prevents its isolation [27]. 

The number of known phosphatases is large and growing, and this short article presents a representative sampling of those for which structural and/or mechanistic data are known, and covers examples of known motifs that nature has evolved to accomplish the hydrolysis of phosphate monoesters. 

Purple Acid Phosphatases. Purple acid phosphatases (PAPs) utilize a dinuclear metal center to catalyze the hydrolysis of phosphate monoesters. The characteristic purple color of these enzymes arises from a charge transfer absorption at about 560 nm, between a tyrosinate ligand and the conserved Fe + found in all PAPs. The second metal ion varies with the source of the enzyme and is always divalent. Mammalian PAPs are monomeric and have Fe -Fe " centers, whereas most plant PAPs are dimeric with Fe " -Zn + centers. A PAP isolated from sweet potato contains an Fe +-Mn + center, the first of its kind in any enzyme (26,27). This novel PAP also differs from others by its greater catalytic efficiency toward both activated and unactivated substrates (27), as well as in its strict requirement for manganese in the divalent site (26). 

The spontaneous hydrolysis of 2-pyridyl phosphate (PP) is a good model for the special mechanism (Scheme 15) for the hydrolysis of phosphate monoester monoanions (M ), which are believed to react via an initial proton transfer equilibrium to form the highly reactive species the proton transfer occurring from a hydroxyl group attached... 

SUPRAMOLECULAR PHOSPHATASE FORMED BY SELF-ASSEMBLY OF BIS(ZN2+-CYCLEN) COMPLEX, CYANURIC ACID, AND COPPER FOR SELECTIVE HYDROLYSIS OF PHOSPHATE MONOESTER IN AQUEOUS SOLUTION... 

Klahn, M., Rosta, E., 8c Warshel, A. (2006). On the mechanism of hydrolysis of phosphate monoesters dianions in solutions and proteins. Journal of the American Chemical Society, 128, 15310. 

Escherichia coli alkaline phosphatase, a dimeric zinc metalloenzyme ( 95,500 Da), binds 2 Zn ions and 1 Mg ion per monomer and functions in the non-specific hydrolysis of phosphate monoester. NMR (mi labeled histidine biosyntheti-cally incorporated into AP in conjunction with substrate NMR and Cd NMR methods were used for the assigmnent of the three Cd resonances to specific sites per monomer and their role in substrate binding. A full account of these studies can be found in the following references [6,25,80,82,201],... 

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