Hydrolysis of phosphate compounds

Table 16.1 The free energies of hydrolysis of phosphate compounds at 298.15 K... 

De Meis, L. (1989). Role of water in the energy of hydrolysis of phosphate compounds—energy transduction in biological membranes. Biochim. Biophys. Acta 973, 333-349. 

Overbrowning of oat cakes brown discoloration of wheat bran Hydrolytic rancidity Hydrolytic rancidity Increase available phosphate Hydrolysis of phosphate compounds Detection of effectiveness of pasteurization Production of nucleotides and nucleosides Detection of effectiveness of blanching In combination with glucose oxidase... 

Table III-1 Rates of Hydrolysis of Phosphate Compounds in Dilute Acid (100°C, 1 N acid)...

Effect of pH on the Standard Transformed Gibbs Energy of Hydrolysis of Phosphate Compounds... 

Calculation of Standard Gibbs Energies of Reaction for Hydrolysis of Phosphate Compounds at 298.15 K and Zero Ionic Strength... 

It is evident that very different types of bonds are split. It is important to remember that these apparent equilibrium constants at 298.15 K and ionic strength 0.25 M are a consequence of the equilibrium constants of chemical reference reactions and p/fs of reactants. Any attempt to interpret these K values has to take into account these two different types of effects. The next two sections explore these effects in the hydrolysis of phosphate compounds. 

Figure 10.1 Standard transformed Gibbs energies of hydrolysis of phosphate compounds and changes in the binding of hydrogen ions as a function of pH at 298.15 K and 0.25 M ionic strength.

See also Substrate Level Phosphorylation, Oxidation as a Metabolic Energy Source, Factors Contributing to Large Energies of Hydrolysis of Phosphate Compounds (from chapter 3)... 

L. de Meis, Role of Water in the Energy of Hydrolysis of Phosphate Compounds—Energy Transduction in Biological Membranes. Biochim. Biophys. Acta, 973,333-349,1989. 

Many mechanistic aspects of the hydrolysis of phosphate esters in protic media remain uncertain. In spite of predictions that racemization at phosphorus should be the final outcome if indeed the (hypothetical) metaphosphate intermediate is involved in the solvolysis of monoesters, the results of several studies on the methanolysis of appropriately O-isotopically labelled compounds are consistent with reactions proceeding with inversion of configuration, as observed for all enzymic and non-enzymic systems so far examined this has resulted in the suggestion that if metaphosphate is actually formed, then it must be in a masked form. 

All these compounds arc selective inhibitors of the serine/threo nine phosphatases PP1 and PP2A.4 Phosphatases catalyze the hydrolysis of phosphates bound to serine or threonine OH groups in en/ymesT and hydrolysis of this type causes the en/ymes to be activated or deactivated. Among other functions these en/ymes play a role in the regulation and control of glycogen metabolism. 

The third enzyme in the pathway, KD0-8-phosphate phosphatase, has been purified to homogeneity (26). Because of its abosolute specificity, it should be a focal point for chemotherapeutic studies. jThe apparent for KD0-8-phosp te was+ etermined to be 5.8 x 10 M in the presence of 1.0 mM Co or Mg. This specific KD0-8-phosphate phosphatase was separated from enzymes, present in crude extracts, having phosphatase activity on other phosphorylated compounds by column chromatography on DGAE-Sephadex (26). Three distinct peaks of activity were detected. Fractions from each peak were pooled and the rates for the hydrolysis of five compounds were measured. Peak A possessed phosphatase activity for D-glucose-6-phosphate, D-arabinose-5-phosphate, D-ribose-5-phosphate and j-nitrophenylphosphate Peak B dephosphorylated D-arabinose-5-phosphate, D-ribose-5-phosphate and D-glucose-6-phos-phate. Peak C, which was well separated from the other two peaks, could only utilize KD0-8-phosphate as a substrate. KD0-8-phos-phate was not hydrolyzed by the phosphatases present in peaks A and B. 

Zr phosphates and phosphites have played a variety of roles in organic transformations, acting as a catalyst support media,550 as heterogeneous catalysts for tetrahydropyranylation of alcohols and phenols,551 and as catalysts for the hydrolysis of phosphodiester compounds.552-556... 

Pantothenic acid is taken in as dietary CoA compounds and dCphosphopantetheine and hydrolyzed by pyrophosphatase and phosphatase in the intestinal lumen to dephospho-CoA, phosphopantetheine, and pantetheine. This is further hydrolyzed to pantethenic acid. The vitamin is primarily absorbed as pantothenic acid by a saturable process at low concentrations and by simple diffusion at higher ones. The saturable process is facilitated by a sodium-dependent multivitamin transporter, for which biotin and lipoate compete. After absorption, pantothenic acid enters the circulation and is taken up by cells in a manner similar to its intestinal adsorption. The synthesis of CoA from pantothenate is regulated by pantothenate kinase, which itself is subject to negative feedback from the products CoA and acyi-CoA. The steps involved were outlined above. Pantothenic acid is excreted in the urine after hydrolysis of CoA compounds by enzymes that cleave phosphate and the cys-teamine moieties. Only a small fraction of pantothenate is secreted into milk and even less into colostrum. 

A cooperative effect of two mononuclear complexes has been observed in the hydrolysis of phosphate mono- or diesters, the reaction order being then two with respect to the metal (343-348). Hydrolysis of methyl para-nitrophenylphosphate diester doubly coordinated to a di-nuclear cobalt(III) complex was reported, and a crystalline compound of dimethylphosphate coordinated to the same cobalt complex was characterized [Co2 (l,4,7-triazacyclononane)2 (0H)2 02P(0CH3)2 ] ... 

During the last decade, information on the organic phosphorus composition of soil solutions and water extracts has been obtained by phosphatase hydrolysis. This technique not only gives structural information on filterable organic phosphorus, but also indicates its potential biological availability. In solution from Scottish upland soils, up to 64% of the filterable organic phosphorus was hydrolysed by non-specific phosphatases (Shand and Smith, 1997), while hydrolysable unreactive phosphorus in water extracts of Australian pasture soils was dominated by phosphate diesters and myo-inositol hexakisphosphate (Turner et al., 2002a). Only small concentrations of labile monoesters were detected in the latter study, possibly due to the rapid hydrolysis of labile compounds by soil phosphatase enzymes. 

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