Phosphomonoesterases

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. 

A method for the direct spectrophotometric determination of dinucleoside monophosphates has been developed which relies on changes in u.v. absorbance after enzymic hydrolysis. - Hydrolytic fission of the dinucleoside monophosphate with a phosphodiesterase causes a change in the u.v. absorbance of the solution allowing the 5 -nucleoside to be estimated. Addition of a phosphomonoesterase to the hydrolysate causes a further change in u.v. absorbance, allowing the 3-nucleoside to be estimated. 

Increased soil phosphatase activity, net plant primary production, total aboveground P Increased phosphomonoesterase activities, increased soil and shoot P... 

No phosphate was released when the fraction was treated with phosphomonoesterase, indicating the presence of a phosphoric diester. Hydrolysis of the unknown KDO derivative (1 M HC1 for 5 h at... 

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). 

Alkaline phosphomonoesterase (EC 3.1.3.1). The existence of a phosphatase in milk was first recognized in 1925. Subsequently characterized as an alkaline phosphatase, it became significant when it was shown that the time-temperature combinations required for the thermal inactivation of alkaline phosphatase were slightly more severe than those required to destroy Mycobacterium tuberculosis, then the target micro-organism for pasteurization. The enzyme is readily assayed, and a test procedure based on alkaline phosphatase inactivation was developed for routine quality control of milk pasteurization. Several major modifications of the test have been developed. The usual substrates are phenyl phosphate, p-nitrophenyl-phosphate or phenolphthalein phosphate which are hydrolysed to inorganic phosphate and phenol, p-nitrophenol or phenolphthalein, respectively ... 

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. 

Diaz-Maurino, T. and Nieto, M. 1976. Milk fat globule membranes. Inhibition by sucrose of the alkaline phosphomonoesterase. Biochim. Biophys. Acta 448, 234-244. Diaz-Maurifio, T. and Nieto, M. 1977. Milk fat globule membranes Chemical composition and phosphoesterase activities during lactation. J. Dairy Res. 44, 483-493. Dowben, R. M., Brunner, J. R. and Philpott, D. E. 1967. Studies on milk fat globule membranes. Biochim. Biophys. Acta 135, 1-10. 

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). 

Horiuchi et al. (2), and Torriani (S) that orthophosphate repressed the formation of a nonspecific phosphomonoesterase in E. coli that research on this enzyme began. This work (2, 3) showed a maximum rate of synthesis of the enzyme occurred only when the phosphate concentration became low enough to limit cell growth. With sufficient phosphate, the amount of active enzyme is negligible. Under conditions of limiting phosphate, alkaline phosphatase accounts for about 6% of the total protein synthesized by the cell (4). 

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. 

Fig. 10. Time course of phosphomonoesterase inactivation by 0.1 mM IC1 at pH 8.1. Other conditions are as described for Fig. 9. From Bobrzecka et al. (60).

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