Phosphomonoesterases, acid

In E. coli GTP cyclohydrolase catalyzes the conversion of GTP (33) into 7,8-dihydroneoptetin triphosphate (34) via a three-step sequence. Hydrolysis of the triphosphate group of (34) is achieved by a nonspecific pyrophosphatase to afford dihydroneopterin (35) (65). The free alcohol (36) is obtained by the removal of residual phosphate by an unknown phosphomonoesterase. The dihydroneoptetin undergoes a retro-aldol reaction with the elimination of a hydroxy acetaldehyde moiety. Addition of a pyrophosphate group affords hydroxymethyl-7,8-dihydroptetin pyrophosphate (37). Dihydropteroate synthase catalyzes the condensation of hydroxymethyl-7,8-dihydropteroate pyrophosphate with PABA to furnish 7,8-dihydropteroate (38). Finally, L-glutamic acid is condensed with 7,8-dihydropteroate in the presence of dihydrofolate synthetase. 

Phosphates of pharmaceutical interest are often monoesters (Sect. 9.3), and the enzymes that are able to hydrolyze them include alkaline and acid phosphatases. Alkaline phosphatase (alkaline phosphomonoesterase, EC 3.1.3.1) is a nonspecific esterase of phosphoric monoesters with an optimal pH for catalysis of ca. 8 [140], In the presence of a phosphate acceptor such as 2-aminoethanol, the enzyme also catalyzes a transphosphorylation reaction involving transfer of the phosphoryl group to the alcohol. Alkaline phosphatase is bound extracellularly to membranes and is widely distributed, in particular in the pancreas, liver, bile, placenta, and osteoplasts. Its specific functions in mammals remain poorly understood, but it seems to play an important role in modulation by osteoplasts of bone mineralization. 

Acid phosphatase (acid phosphomonoesterase, EC 3.1.3.2) also catalyzes the hydrolysis of phosphoric acid monoesters but with an acidic pH optimum. It has broad specificity and catalyzes transphosphorylations. Acid phosphatases are a quite heterogeneous group with monomeric, dimeric, larger glycoprotein, and membrane-bound forms. Acid phosphatase activity is present in the heart, liver, bone, prostate, and seminal fluid. Prostate carcinomas produce large quantities of acid phosphatase, and the enzyme is, therefore, used as a biomarker [141]. 

This enzyme [EC 3.1.3.2], also referred to as acid phos-phomonoesterase, phosphomonoesterase, and glycero-phosphatase, catalyzes the hydrolysis of an orthophos-phoric monoester to generate an alcohol and... 

Another phosphomonoesterase family, the purple acid phosphatases, have been attracting interest, since they contain a mixed-valence binu-clear iron(II/III) center (26). Although the exact roles of iron(II) and iron(III) have not been clarified yet, it has recently been reported that the direct nucleophilic attack of Fe111—OH- at the phosphate P atom is the most likely mechanism (27). 

Alkaline phosphomonoesterase Hydrolysis of phosphoric acid esters Index of pasteurization... 

Milk contains several phosphatases, the principal ones being alkaline and acid phosphomonoesterases, which are of technological significance, and ribonuclease, which has no known function or significance in milk. The alkaline and acid phosphomonoesterases have been studied extensively (see Andrews (1993) for references). 

Acid phosphomonoesterase (EC 3.1.3.2). Milk contains an acid phosphatase which has a pH optimum at 4.0 and is very heat stable (LTLT pasteurization causes only 10-20% inactivation and 30 min at 88°C is required for full inactivation). Denaturation of acid phosphatase under UHT conditions follows first-order kinetics. When heated in milk at pH 6.7, the enzyme retains significant activity following HTST pasteurization but does not survive in-bottle sterilization or UHT treatment. The enzyme is not activated by Mg2+ (as is alkaline phosphatase), but it is slightly activated by Mn2+ and is very effectively inhibited by fluoride. The level of acid phosphatase activity in milk is only about 2% that of alkaline phosphatase activity reaches a sharp maximum 5-6 days post-partum, then decreases and remains at a low level to the end of lactation. 

Potentiometric titration of the teichoic acid from strain 8191 reveals the presence of a terminal phosphomonoester group, and indicates a chain length of 20-22 residues. This phosphomonoester residue is resistant to the action of phosphomonoesterase, presumably because of the neighboring, bulky, sugar substituents. 

The sedimentation coefficient of spleen exonuclease, measured by centrifugation in a sucrose density gradient, using cytochrome c as the reference protein, was 4.6 S 11). The enzyme is eluted from Sephadex G-100 between acid phosphomonoesterase (s = 5.6 S) and acid DNase (s = 3.4 S). 

Minute amounts of the acid phosphomonoesterases have also been found to occur in the pancreas, in skeletal and heart muscle, and in the mucosa of the small intestines. 

Relative Rate of Hydrolysis of Several Substrates by Spleen Acid Phosphomonoesterase -6... 

R. Weimberg and W. L. Orton (1965). Synthesis and breakdown of the polyphosphate fraction and acid phosphomonoesterase of Saccharomyces mellis and their location in the cell. J. Bacteriol., 89, 740-742. 

Alkaline and acid phosphatase are organ-specific enzymes that are assayed in the diagnosis of many diseases. These activities are phosphomonoesterases that dephosphorylate a number of compounds, including nucleoside monophosphates, to their respective nucleosides and free phosphates. However, such dephosphorylations have traditionally been assayed with 4-nitrophenyl... 

An approximate idea of the distribution of acid phosphatase activity in human tissues, regardless of the nature of the acid phosphatase, may be obtained from the studies of Reis (R2) on 5 -nucleotidase and other phosphomonoesterases. He prepared aqeuous homogenates of postmortem tissue in the proportion of 20 parts of water to one of tissue, allowed these to autolyze for 2 days at room temperature, centrifuged the material, and employed the supernatant fluid. The assay mixture consisted of 0.4 ml of a suitable buffer, 0.1 ml of 0.005 Af phenyl phosphate as substrate, and 0.1 ml of tissue extract. The enzyme activity was expressed as micrograms of phosphorus hydrolyzed per hour per milligram of wet... 

Ostrowski, W., Wasyl, Z., Weber, M., Guminska, M., and Luchter, E., The role of neuraminic acid in the heterogeneity of acid phosphomonoesterase from the human prostate gland. Biochim. Biophys. Acta 221, 297-306 (1970). 

T3. Tsuboi, K. K., and Hudson, P. B., Acid phosphatase. III. Specific kinetic properties of highly purihed human prostatic phosphomonoesterase. Arch. Biochem. Biophys. 55, 191-205 (1955). 

Gulland and Jackson confirmed that phosphomonoesterase liberates 7%, or less, of the phosphoric acid from ribosenucleic acid. They therefore concurred with Takahashi that this kind of ribosenucleic acid contains no phosphomonoester group and that each phosphorus atom is present as a disubstituted phosphoryl group, but they pointed out that this is not necessarily a di-ester group. The liberation of 7%, or less, of the total phosphorus is in accord with the idea of a polymerized tetranucleotide 25% of the phosphorus in the simple tetranucleotide (VII) should be hydrolyzable by phosphatase. 

IMP and GMP are non-hygroscopic salts. They are stable towards heat (up to 120°C) and acidity (optimum pH is 5-7) [2, 8, 9]. Taste thresholds in aqueous solution are 25-120 ppm and 12-35 ppm for IMP and GMP, respectively [2, 8, 10]. Use of IMP and GMP in liquid foods may present some problems. Many vegetable and animal foods contain phosphomonoesterases which can easily split the phosphomonoester linkage of the ribonucleotides and the flavour improving effect is lost. From a practical standpoint, these enzymes should be inactivated by heating to 85°C before the addition of IMP or GMP. 

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