Phosphatase phosphohydrolases

Lipid phosphate phosphohydrolases (LPPs), formerly called type 2 phosphatidate phosphohydrolases (PAP-2), catalyse the dephosphorylation of bioactive phospholipids (phosphatidic acid, ceramide-1-phosphate) and lysophospholipids (lysophosphatidic acid, sphingosine-1-phosphate). The substrate selectivity of individual LPPs is broad in contrast to the related sphingosine-1-phosphate phosphatase. LPPs are characterized by a lack of requirement for Mg2+ and insensitivity to N-ethylmaleimide. Three subtypes (LPP-1, LPP-2, LPP-3) have been identified in mammals. These enzymes have six putative transmembrane domains and three highly conserved domains that are characteristic of a phosphatase superfamily. Whether LPPs cleave extracellular mediators or rather have an influence on intracellular lipid phosphate concentrations is still a matter of debate. 

SIP is formed from sphingosine by sphingosine kinases (SphKs). Degradation of SIP occurs either reversibly by lipid phosphate phosphohydrolases (LPPs) and SIP phosphatases (SPPs), or irreversibly by SIP lyase (SPL) (Fig. 1). The localization of SIP production is highly important since SIP plays a role both as extracellular mediator and as intracellular... 

McGill and Cole (1981) suggested that the concentration of available P in the soil depended on biochemical mineralization, i.e., mineralization by extracellular enzymes, which does not provide energy to organisms and depends on the amount of enzymes present. This is controlled by the need for P. Thus, organic P input into the soil only influences the size of the total pool, while plants, microbes, and mycorrhiza can make P available by releasing phosphatases and phosphohydrolases into the soil. Phosphatase excretion has been used as an indicator of the P status of plants (Johnson et al. 1999 Phoenix et al. 2004). 

This enzyme [EC 3.1.3.26], also known as phytase, phy-tate 6-phosphatase, and myo-inositol-hexaphosphate 6-phosphohydrolase, catalyzes the hydrolysis of myoinositol hexakisphosphate to produce 1-myo-inositol... 

Acid phosphatase or orthophosphoric monoester phosphohydrolase (EC 3.1 3.2) activity is widespread throughout nature. Hydrolysis of a variety of orthophosphate esters as well as transphosphorylation reactions are catalyzed by enzymes from many sources. Table I illustrates their ubiquitous nature. 

Glucose-6-phosphatase (D-glucose-6-phosphate phosphohydrolase, EC 3.1.3.9) is a unique enzyme in several respects. It is the only principal... 

The enzyme has been reviewed briefly by Byrne in the preceding edition of The Enzymes (1) and elsewhere (2) it has also been reviewed by Manners (3), and by Swanson (4) and Nordlie and Arion (5) in two volumes of Methods in Enzymology. The roles played by hepatic glucose-6-phosphatase in regulating carbohydrate metabolism have been described in excellent reviews by Cahill et al. (0) and by Ashmore and Weber (7). The latter work also contains a comprehensive review of catalytic properties of the phosphohydrolase activity of the enzyme covering studies carried out prior to 1958. Glucose-6-phosphatase, along with a number of other enzymes involved in carbohydrate metabolism, has also been reviewed in Japanese (8). 

Subcellular Distribution of Inorganic Pyrophosphatase, PPi-GLUcosE Phosphotransferase, and Glucose-6-P Phosphohydrolase Activities of Rat Liver Microsomal Glucose-6-Phosphatase ... 

Fig. 3. Proposed mechanism involving hydrolytic and synthetic activities of glucose-6-phosphatase in the transport of glucose between intracellular and extracellular compartments. The shaded area represents the cross-sectional view of endoplasmic reticulum. E and E" are modified forms of glucose-6-phosphatase displaying principally phosphohydrolase and principally phosphotransferase activities, respectively. Differential influences of the intra- and extracellular milieu are postulated to maintain molecules of the enzyme selectively as E or E". Additional details are given in Section II,D.

Comparison of Levels of Phosphotransferase and Phosphohydrolase Activities of Glucose-6-Phosphatase in Liver, Kidney, and Small Intestine of Rabbit"... 

As discussed briefly in Section I,A, glucose-6-phosphatase is now known to be a multifunctional enzyme capable of catalyzing potent phosphotransferase as well as phosphohydrolase reactions [see Eqs. (1)—(4) ]. Compounds demonstrated to function as effective phosphoryl donors include fructose-6-P (30), mannose-6-P (40), PPi (35-38), a variety of nucleosidetriphosphates and nucleosidediphosphates—most effectively CTP, CDP, deoxy-CTP, ATP, ADP, GTP, GDP, and ITP (41, 45)— carbamyl-P (43), phosphoramidate (44), phosphopyruvate (42, 43) and glucose-6-P itself (30, 31). The various phosphoryl donors are also hydrolyzed by action of the enzyme (see preceding references). Eqqa-tions (1)—(4), which describe these various activities, are given in Section I,A. 

Recent studies indicate that the various phosphohydrolase and phosphotransferase activities of glucose-6-phosphatase are affected by numerous metabolites (see Table X and Sections II,C and III,D,4). The possible significance of observed activation or inhibition by a number of these compounds in vitro relative to regulation of both types of activity of the enzyme in vivo has been considered in a number of instances. Possible modes of control of net glucose release, involving the regulation by a variety of factors, of both hydrolytic and synthetic activities of the enzyme, have been discussed in considerable detail in earlier reviews by the author (9, 10). 

The assays for the enzyme synthesis of sulfogalactosyl-glycerolipid, sulfatides and galactocerebrosides were carried out as previously described respectively by Subba Rao, et al. (28) Sarlieve, et al. 05, 29), and Neskovic, et al. (30). The assay for 2, 3 cyclic nucleotide phosphohydrolase was performed according to the method of Prohaska, et al. (31). EL coli. alkaline phosphatase type III-S, 2, 3 -cAMP, and sodium deoxycholate were obtained from Sigma (St. Louis, Mo.). Protein was determined by the method of Lowry, et al. (32) with crystalline bovine serum albumin as the standard. 

Phytase phosphatase Aspergillus niger var. (1) myo-inositol- hexakisphosphate-3- phosphohydrolase (2) orthophosphoric-mono ester phosphohydrolase 3.1.3.8 3.1.3.2... 

Protein phosphorylation alters protein ligand binding and/or catalytic functions and hence specific cellular processes, this representing the cellular response to the stimulus of the original primary messenger . The signalling system must be reversible and the protein phosphorylation step of the stimulus-response pathway is reversed through the action of phosphoprotein phosphatases (PPs), which are phosphohydrolases that catalyse the hydrolytic dephosphorylation of proteins ... 

The conversion of phosphorylase b to a involves the addition of the terminal phosphate of ATP. The phosphate is then removed as the enzyme is converted back to phosphorylase b under the catalytic influence of phosphorylase phosphatase (EC 3.1.3.17 phosphorylase phosphohydrolase). Phosphorylase phosphatase from rabbit skeletal muscle has been purified 700-fold [86]. 

Orthophosphoric-monoester phosphohydrolase (alkaline optimuni) v - Alkaline phosphatase ALP... 

Under the name of acid phosphatase (EC 3.1.3.2 orthophos-phoric-monoester phosphohydrolase [add optimum] AGP) are included aU phosphatases with optimal activity below a pH of 7.0. 

The problem of elucidating the mechanism of catalysis by alkaline phosphatase has been attacked by a number of workers from different directions from kinetic studies and modification of key linkages in the substrates and enzyme to the visualization of mechanism through models. Studies of related phosphohydrolases are relevant (A19, K26, L20, Pll, P12). 

In contrast to phosphohydrolases, the phosphatase activity of enzymes which non-hydrolytically catalyse the transfer of phosphate groups can be stimulated by vanadate. Vanadate can spontaneously form esters with unphosphorylated substrates such as sugars. These vanadate esters act as alternative substrates for mutases and isomerases, stimulating their phosphatase activity. Examples are phosphoglucomutase, which catalyses the mutation (phosphate shift) between glucose-1-phosphate and glucose-6-phosphate, and phosphoribose isomerase, which catalyses the isomerisation between ribose-5-phosphate and ribulose-5-phosphate.P ]... 

In vivo, cleavage of P-0 bonds are performed by enzymes such as phosphatases, phosphodiesterases, phosphohydrolases, nucleases, DNases and RNases (see Section 13.1.1). In vitro, cleavage of a P- O bond is often a trivial synthetic step. Even for an easy step, enzymes attract increasing attention. The enzymatic reactions are preferred when regio- or stereoselectivity is required, and when the substrates are temperature or pH sensitive. Many phosphate analogs have been tested as substrates of enzymes that hydrolyze phosphoryl groups. These analogs are often accepted as substrates for the enzymes, and such reactions could be synthetically valuable. Typical examples are presented in the tables. 

One of the best examples of an enzymatic dephosphorylation for a synthetic purpose is shown in the entry 5 ofTable 13-6. A 5 -ribonucleotide phosphohydrolase was used in the synthesis of (-)-aristeromycin, a carbocyclic analog of adenosine. The (-)-enantiomer of aristeromycin shows some cytostatic and antiviral activity, while the (+)-enantiomer is inactive. The racemate ( )-5 -phosphorylated aristeromycin was resolved by selective hydrolysis of the (-)-enantiomer with the hydrolase. The (-)-alcohol and the (+)-5 -phosphate derivative were separated easily on a silica gel column. Hydrolysis of the (-t-)-enantiomer with calf intestinal phosphatase yielded pure (+)-alcohol. 

Phytase. Phytate 3-phosphatase. Myo-inositol-hexaphosphatc 3-phosphohydrolase. 

Stereochemical studies have been performed on phosphohydrolases, which are considerably less well structurally characterized than alkaline phosphatase from... 

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