Phosphatase-catalyzed reaction

Levine, D., Reid, T. W., Wilson, I. B. The free energy of hydrolysis of the phosphoryl-enzyme intermediate in alkaline phosphatase catalyzed reactions. Biochemistry 1969, 8, 2374—2480. 

Zhao Y, Wu L, Noh SJ et al (1998) Altering the nucleophile specificity of a protein-tyrosine phosphatase-catalyzed reaction. Probing the function of the invariant glutamine residues. J Biol Chem 273 5484-5492... 

Scheme 19.14 One-pot process based on combination of an aldolase-catalyzed reaction, spontaneous cyclization and a phosphatase-catalyzed reaction.

Craig D B, Arriaga E A, Wong J C Y, Lu H and Dovichi N J 1996 Studies on single alkaline phosphatase molecules reaction rate and activation energy of a reaction catalyzed by a single molecule and the effect of thermal denaturation—the death of an enzyme J. Am. Chem. See. 118 5245-53... 

Enzymes are powerful catalysts. Enzyme-catalyzed reactions are typically 10 to times faster than their uncatalyzed counterparts (Table 16.1). (There is even a report of a rate acceleration of >10 for the alkaline phosphatase-catalyzed hydrolysis of methylphosphate )... 

Alkaline phosphatase catalyzes the dephosphorylation of a mmber of artificial substrates ( ) including 3-glycerophosphate, phenylphosphate, p-nitrophenylphosphate, thymolphthalein phosphate, and phenolphthalein phosphate. In addition, as shown recently for bacterial and human enzymes, alkaline phosphatase simultaneously catalyzes the transphosphorylation of a suitable substance which accepts the phosphoryl radical, thereby preventing the accumulation of phosphate in the reaction mediim (25). 

The majority of the diethyl phosphate and -nitrophenol formed in the mammalian metabolism of parathion is undoubtedly derived by the action of esterases or phosphatases ( ) on paraoxon formed from parathion in a cytochrome P-450-catalyzed reaction. However, a significant portion of the diethyl phosphate and -nitrophenol must also be the result of the attack of water on the intermediate S-oxide of parathion ( ). 

Enzymes often are known by common names obtained by adding the suffix -ase to the name of the substrate or to the reaction that they catalyze. Thus, glucose oxidase is an enzyme that catalyzes the oxidation of glucose glucose-6-phosphatase catalyzes the hydrolysis of phosphate from glu-cose-6-phosphate and urease catalyzes the hydrolysis of urea. Common names also are used for some groups of enzymes. For example, an enzyme that transfers a phosphate group from ATP to another molecule is usually called a kinase, instead of the more formal phosphotransferase. ... 

Pectinesterase and limonin D-ring lactonase are the only enzymes known to catalyze reactions that adversely affect the quality of citrus juices. Bruemmer et al. (64) listed other enzymes that have been detected in citrus juices and described some of the reactions that can occur in the juices. None of the reactions appear to noticeably affect the quality of commercial juices. Freshly extracted citrus juices contain esterase (EC 3.1.1.1) (65, 66) and phosphatase (EC 3.1.32) (66, 67) activities. Native substrates in orange juice for peroxidase... 

Enzymes are biocatalysts constructed of a folded chain of amino acids. They may be used under mild conditions for specific and selective reactions. While many enzymes have been found to be catalytically active in both aqueous and organic solutions, it was not until quite recently that enzymes were used to catalyze reactions in carbon dioxide when Randolph et al. (1985) performed the enzyme-catalyzed hydrolysis of disodium p-nitrophenol using alkaline phosphatase and Hammond et al. (1985) used polyphenol oxidase to catalyze the oxidation of p-cresol and p-chlorophenol. Since that time, more than 80 papers have been published concerning reactions in this medium. Enzymes can be 10-15 times more active in carbon dioxide than in organic solvents (Mori and Okahata, 1998). Reactions include hydrolysis, esterification, transesterification, and oxidation. Reactor configurations for these reactions were batch, semibatch, and continuous. 

Studies of the oxidation of organic sulfides with amino acid-derived ligands in acetonitrile revealed very little difference between the mechanism of their oxidation and that of halides, except for one major exception. Despite the fact that acid conditions are still required for the catalytic cycle, hydroxide or an equivalent is not produced in the catalytic cycle, so no proton is consumed [48], As a consequence, there is no requirement for maintenance of acid levels during a catalyzed reaction. Peroxo complexes of vanadium are well known to be potent insulin-mimetic compounds [49,50], Their efficacy arises, at least in part, from an oxidative mechanism that enhances insulin receptor activity, and possibly the activity of other protein tyrosine kinases activity [51]. With peroxovanadates, this is an irreversible function. Apparently, there is no direct effect on the function of the kinase, but rather there is inhibition of protein tyrosine phosphatase activity. The phosphatase regulates kinase activity by dephosphorylating the kinase. Oxidation of an active site thiol in the phosphatase prevents this down-regulation of kinase activity. Presumably, this sulfide oxidation proceeds by the process outlined above. 

Bisphosphoglycerate is synthesized from 1,3-bisphosphoglycerate, a reaction catalyzed by 2.3-bisphosphoglycerate synthase. The enzyme 2,3-bisphosphoglycerate phosphatase catalyzes the hydrolysis of 2,3-bisphosphoglycerate to 3-phosphoglycerate. 

Figure 8 Kinase-catalyzed phosphorylation and phosphatases-catalyzed dephosphorylation reactions, (a) Catalytic mechanism of protein kinases (b) Catalytic mechanism of bimetallic pSer/pThr or dual specifity protein phosphatases (c) Catalytic mechanism of pTyr phosphatases.

Other enzymes are also useful indices of liver pathology. Serum alkaline phosphatase is often a useful indicator of liver and bone disease. The alkaline phosphatases are a diverse group of enzymes that catalyze reactions in which a phosphate is removed from a phosphate ester, especially at an alkaline pH. Physicians don t care about this. They do care that serum alkaline phosphatase levels often rise with bone breakdown (as in tumor infiltration) and in liver disease, especially where tliere is obstruction of the bile duct. Acid phosphatase is particularly rich in the prostate. A rise in its serum levels provides a test as to the presence of prostate carcinoma. This test has largely been replaced by assay for Prostate Specific Antigen (PSA), a serine protease that is elevated in prostatic carcinoma. 

Detection limits in EIA are ultimately determined by how low one can measure the label s concentration via an activity assay. Sensitivity in such a kinetic determination is dependent upon the turnover number of the enzyme molecule and the method employed to detect the product of the catalyzed reaction. Purified urease obtained from Sigma Chemical Co. has considerably higher activity on a molar basis (international units per mole of enzyme) than the best available commercial preparations of some other common enzyme labels such as alkaline phosphatase, /8-galactosi-dase, peroxidase, - and glucose oxidase. This is due to the high mo-... 

The direct detection of electrochemical labels entails problems with sensitivity. For this reason the majority of electrochemical immimoassay development has focused on the measurement of enzyme labels by detection of eiectroactive products arising from enzyme catalyzed reactions. A wide variety of enzyme labels have been used for electrochemical immunoassays. These include glucose oxidase, glucose-6-phosphate dehydrogenase and alkaline phosphatase. ... 

The Escherichia coli alkaline phosphatase (li coli AP) is the most extensively studied phosphatase, and perhaps the most studied two-metal ion catalyst.68,91 95 The AP-catalyzed reaction proceeds via an intermediate in which a serine residue (Ser-102 in E. coli AP) is phosphorylated. Thus, the stereochemical outcome of the overall reaction is retention. The hydrolysis of the intermediate by water to produce inorganic phosphate competes with phosphoryl transfer to other acceptors such as alcohols or nucleophilic buffers if such are present in solution. The rate-limiting step... 

With enzyme determinations, standards for calibration purposes and for checking of instrumental performance make use of separately prepared solutions of one of the reactants or the products of the enzyme-catalyzed reaction. For instance, a solution of phenol may be standardized and thereafter used itself as the standard in determinations of acid and alkaline phosphatase, in methods employing phenyl phosphate as substrate and depending on the measurement of the amount of phenol liberated. This standard phenol solution, however, cannot be taken through all the steps in the determination of phosphatase, and a separate control solution must be used to check the performance of the overall technique if this control were omitted, it would be possible, for instance, for a buffer to be incorrectly prepared and for erroneous levels of phosphatase activity to be found. There is no substitute, therefore, in the control of enzyme determinations for the inclusion of a sample (of serum, urine, etc.) previously investigated for its level of enzyme activity. For long-term monitoring of an enzyme method, the repeated analysis of aliquots of a standardized enzyme preparation is most useful, provided... 

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