Hydrolysis phosphates

Calculate the free energy change for acetyl phosphate hydrolysis in a solution of 2 mM acetate, 2 mM phosphate, and 3 iiM acetyl phosphate. 

Interestingly, however, the mechanisms of the two phosphate hydrolysis reactions in steps 9 and 11 are not the same. In step 9, water is the nucleophile, but in the glucose 6-phosphate reaction of step 11, a histidine residue on the enzyme attacks phosphorus, giving a phosphoryl enzyme intermediate that subsequently reacts with water. 

Once aryl phosphite has oxidized into phosphate followed by the catalytic decomposition of hydroperoxide [6,10,19,20], The catalyst is obviously stable, since additional hydroperoxide introduced into the system immediately breaks down [10]. Repeatedly, ROOH decomposes via the acid-catalyzed reaction with the products of phosphate hydrolysis acting as catalysts [6,10],... 

Figure 6.8. Cyclic and non-cyclic inositol phosphates. Hydrolysis of phosphatidyl 4,5-bisphosphate (PIP2) by phospholipase C can generate cyclic and non-cyclic inositol phosphates.

Magnetic resonance techniques have again been popular for studying enzymes which are involved in phosphate hydrolysis and transfer. 31P or 19F N.m.r.1-2 and spinlabelling3 have all been used to study the interaction of substrates with these enzymes, while affinity labelling4 5 6 7 is another technique which has been used to obtain information about the sequence and conformation of amino-acid chains at the active sites of enzymes. Recently, these experimental methods have been applied to the study of cell membranes,6-7 and these are mentioned in a new series of books concerned with enzymes in biological membranes.8 A new journal, Trends in Biochemical Sciences, which contains concise, up-to-date reviews on these and other topics is published by Elsevier on behalf of the International Union of Biochemistry. 

The turnover reaction of hydrolysis of 2, 3 -CMP could be made negligibly slow at temperatures below -60°C at pH 3-6 in 70% methanol, and below -35°C at pH 2.1. The rate of the catalytic reaction using crystalline enzyme was found to be 50-fold slower than that of dissolved enzyme for cyclic phosphate hydrolysis, and 200-fold slower for dinucleotide hydrolysis (presumably the greater reduction for the larger substrate reflects increased diffusional hindrance by the small solvent chan-... 

AGIRE computer program for, 249, 79-81, 225-226 comparison to analysis based on rates, 249, 61-63 complex reactions, 249, 75-78 experimental design, 249, 84-85 inhibitor effects, 249, 71-75 potato acid phosphatase product inhibition, 249, 73-74 preliminary fitting, 249, 82-84 prephenate dehydratase product inhibition, 249, 72-73 product inhibition effects, 249, 72-73 prostate acid phosphatase phenyl phosphate hydrolysis, 249, 70 reactions with two substrates, 249, 75-77 reversible reactions, 249, 77-78 with simple Michaelian enzyme, 249, 63-71 [fitting equations, 249, 63] with slow-binding inhibitors, 249, 88 with unstable enzymes, for kinetic characterization, 249, 85-89. 

Lemaire et al. have developed a efficient fructose-1,6-bisphosphate aldolase (FBPA)-mediated synthesis of aminocyclitol analogs of valiolamine [34], This one-pot route involves the formation of two C—C bonds where four stereocenters are created. The first C—C bond formation reaction is catalyzed by the aldolase, coupling DHAP to nitrobutyraldehydes the other one is the result of a highly stereoselective intramolecular Henry reaction occurring on the intermediate nitroketone under acidic conditions during the aldolase-catalyzed reaction and phytase-catalyzed phosphate hydrolysis coupled step (Scheme 4.13). 

Alkali diphosphates are practically stable in alkaline and neutral solutions, but they are more and more rapidly hydrolyzed with decreasing pH. Over the whole pH range, however, they are more stable, under the same conditions, than all other condensed phosphates. Hydrolysis is accelerated by an increasing temperature or ionic strength (44, 846). The table below shows the dependence of the rate constant for the hydrolysis on pH at... 

Metal ion catalysis of salicyl phosphate hydrolysis is much more complicated than that of Sarin, since the former substrate can combine with metal ions to give stable complexes, and some of the complexes formed do not constitute pathways for the reaction. In addition the substrate undergoes intramolecular acid-base-catalyzed hydrolysis which is dependent on pH because of its conversion to a succession of ionic species having different reaction rates. Therefore a careful and detailed equilibrium study of proton and metal ion interactions of salicyl phosphate would be required before any mechanistic considerations of the kinetic behavior in the absence and presence of metal ions can be undertaken. 

Figure 3. Mechanism of salicyl phosphate hydrolysis in presence and absence of...

To determine the nature of the catalysis of salicyl phosphate hydrolysis by metal chelates, two diamine-Cu(II) chelates were selected for detailed study, N-/ -hydroxyethylethylenediamine-Cu(II) ion (XXV) and a,a -bipyridine-Cu(II) ion (XXVI) (II). 

Of special interest is the comparison of the inactivity of bipyridine-Cu(II) as a catalyst in salicyl phosphate hydrolysis, with its strong catalytic effect on the hydrolysis of dicarboxyphenyl-2-phosphate. A comparison of formulas XXVII with XXXIV and XXXVI shows that mixed complex formation of Cu+2 with salicyl phosphate and bipyridine would prevent attack of the phosphate group via the proposed mechanism. The formation of the analogous mixed chelate with DCPP (XXXIV and XXXVI) would produce a reaction intermediate for the reaction, since the metal ion would tie up one of the carboxylate ions but leave... 

Alkaline phosphatase (AP) is a (Znn)2-containing phosphomonoester-ase that hydrolyzes phosphomonoesters (RO—POf-) at alkaline pH (7). Ser102 under the influence of one of the zinc(II) ions at the active center 1 (Fig. 2) is directly involved in phosphate hydrolysis (8). On the basis of X-ray structure and NMR studies (9), the mechanism now accepted is that the phosphate substrate, initially recognized by cooperative... 

The iron(II)-iron(III) form of purple acid phosphatase (from porcine uteri) was kinetically studied by Aquino et al. (28). From the hydrolysis of a-naphthyl phosphate (with the maximum rate at pH 4.9) and phosphate binding studies, a mechanism was proposed as shown in Scheme 6. At lower pH (ca. 3), iron(III)-bound water is displaced for bridging phosphate dianion, but little or no hydrolysis occurs. At higher pH, the iron(III)-bound OH substitutes into the phosphorus coordination sphere with displacement of naphthoxide anion (i.e., phosphate hydrolysis). The competing affinity of a phosphomonoester anion and hydroxide to iron(III) in purple acid phosphatase reminds us of a similar competing anion affinity to zinc(II) ion in carbonic anhydrase (12a, 12b). 

While there have been a considerable number of structural models for these multinuclear zinc enzymes (49), there have only been a few functional models until now. Czamik et al. have reported phosphate hydrolysis with bis(Coni-cyclen) complexes 39 (50) and 40 (51). The flexible binuclear cobalt(III) complex 39 (1 mM) hydrolyzed bis(4-nitro-phenyl)phosphate (BNP-) (0.05 mM) at pH 7 and 25°C with a rate 3.2 times faster than the parent Coni-cyclen (2 mM). The more rigid complex 40 was designed to accommodate inorganic phosphate in the in-temuclear pocket and to prevent formation of an intramolecular ju.-oxo dinuclear complex. The dinuclear cobalt(III) complex 40 (1 mM) indeed hydrolyzed 4-nitrophenyl phosphate (NP2-) (0.025 mM) 10 times faster than Coni-cyclen (2 mM) at pH 7 and 25°C (see Scheme 10). The final product was postulated to be 41 on the basis of 31P NMR analysis. In 40, one cobalt(III) ion probably provides a nucleophilic water molecule, while the second cobalt(III) binds the phosphoryl group in the form of a four-membered ring (see 42). The reaction of the phosphomonoester NP2- can therefore profit from the special placement of the two metal ions. As expected from the weaker interaction of BNP- with cobalt(in), 40 did not show enhanced reactivity toward BNP-. However, in the absence of more quantitative data, a detailed reaction mechanism cannot be drawn. 

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