Phosphoesterase Activity

In addition to the Zn(II) complexes attempts were made to prepare the Co(II) derivatives of CH3HL4 and CH3HL5. It was anticipated that the Co(II) complexes would permit a more detailed spectroscopic analysis and, by analogy to the 

Due to their sensitivity to oxygen for the MCD measurements, the complexes were prepared in situ in degassed ethanol and immediately analyzed (the complexes 

7 Asymmetric Zn(II) Complexes as Structural and Functional Models for GpdQ 

The MCD spectrum of [Co2(CH3L5)(CH3COO)2] in ethanol is shown in Fig. 7.19. As was observed with the Co(II) complex of the ligand CH3HL4, six-coordinate Co(II) transitions dominate the spectmm. It is intriguing that despite the 

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This is an emerging field that has not reached its final position yet. Members of the novel class of FCP, SCP, and HAD phosphatases require Mg2+ for catalysis. An aspartate residue within the active site signature motif (DxDx(T/V)) is essential to form an acyl-phosphate intermediate. Many members of the the HAD (haloacid dehalogenase) superfamily have phosphoesterase activity [3]. Some of those protein phosphatases act on... 

Meanwhile other experiments have been carried out to isolate DNA molecules with either RNA- or DNA-phosphoesterase activity [69-71,142,143]. Since Mg +-dependent rather than Pb +-dependent cleavage is compatible with intracellular conditions and thus, more suitable for possible medical applications, deoxyribozymes were selected that used Mg + instead of Pb for cleavage [112]. One optimized deoxyribozyme that emerged in this selection showed a cleavage rate of 0.01 min and was also capable of intermolecular cleavage. 

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. 

To mimic many phosphoesterases activated by two or more metal ions, several artificial phosphoesterases have been devised by linking two metal centers with a spacer group. " For example, two triaza ligands were linked by hydroxo (2) or a biphenyl (3) spacer. The dimetallic complexes of the bistriaza ligands... 

Parts of this Chapter have been reprinted with permission from (L.J. Daumann et al.. Synthesis, Magnetic Properties, and Phosphoesterase Activity of Dinuclear Cobalt(II) Complexes. Inorganic Chemistry 2013 52(4), 2029-2043). Copyright (2013) American Chemical Society and in L.J. Daumann et al., Dinuclear Cobalt(II) Complexes as Metallo-f-lactamase Mimics. Eur. J. Inorg. Chem. 2013, 17, 3082-3089. 

L.J. Daumann, P. Comba, J. Larrabee, R. Stranger, G. Cavigliasso, G. Schenk, L.R. Gahan Synthesis, Magnetic Properties and Phosphoesterase Activity of Binuclear Cobalt(II) Complexes Inorg. Chem. 2013, 52 (4), 2029-2043. 

Tymecki, L., K. Strzelak, and R. Koncki. 2013. Biparametric multicommutated flow analysis system for determination of human serum phosphoesterase activity. Anal. Chim. Acta 797 57-63. 

The present volume is the fourth in the series and covers the topics lithium in biology, the structure and function of ceruloplasmin, rhenium complexes in nuclear medicine, the anti-HIV activity of macrocyclic polyamines and their metal complexes, platinum anticancer dmgs, and functional model complexes for dinuclear phosphoesterase enzymes. The production of this volume has been overshadowed by a very sad event—the passing away of the senior editor, Professor Robert W. Hay. It was he who conceived the idea of producing this series and who more than anyone else has been responsible for its continuation. A tribute by one of his many friends, Dr. David Richens, is included in this Volume. 

Nucleoside 2 (or 3 ),5 -diphosphates have been isolated by degradation of certain coenzymes, as well as from hydrolyzates of nucleic acids. Adenosine 3, 5 -diphosphate (see p. 320) has been isolated by enzymic hydrolysis of coenzyme A and from active sulfate (adenosine 3 -phosphate 5 -phosphosulfate). Adenosine 2, 5 -diphosphate was shown to be present in the adenylic acid moiety of the coenzyme adenine-nicotinamide dinucleotide phosphate which, by treatment with a 5 -nucleotidase from potatoes, is converted into adenosine 2 -phosphate. Adenosine 3, 5 -di-phosphate is reported to play a role as a cofactor in the bioluminescence of Renilla reniformis (pansy) Ribonucleic acid carrying a terminal 5 -phos-phate group yields ribonucleoside 3, 5 -diphosphates on digestion with phosphoesterases. ... 

Fig. 4.4 Ligands employed to mimic the active site residues of phosphoesterases...

The presence of a second Co(III) center was suggested to be responsible for a 26-fold increase in the rate of hydrolysis compared to that observed for the corresponding mononuclear complex [27]. It was proposed that the coordinated PNPP was cleaved by an intramolecular attack of a terminal bound hydroxide. Since Sargeson s early work other examples of functional or spectroscopic model complexes for several classes of phosphoesterases enzymes have been reported [28-36], however, only a few use cobalt. The Co(III)Co(Ill) complex with a phenolate based ligand (Fig. 6.4b) showed activity in phosphomonoester cleavage and a bridging coordination of the substrate was confirmed with P NMR [37]. 

C02EtH3Ll and C02EtHL2 only differ in R" and allow comparison of the phosphoesterase-like activity in the presence and absence of alcohol nucleophiles. The model substrate BDNPP will be used. Also the ability of the complexes derived from these two ligands to hydrolyze substrates other than organophosphates will be investigated using the p-lactam substrates nitrocefin and penicillin G. 

The activity towards organophosphoesters using the substrate BDNPP was investigated. All complexes are good functional mimics for phosphoesterase enzymes and show one pKa relevant for hydrolysis (Fig. 6.27a and b Table 6.9). 

In order to generate more structurally relevant biomimetics for dinuclear metallohydrolases much effort has been devoted to the synthesis of asymmetric ligands. These ligands are considered to be more suitable models for the asymmetric coordination environment found in enzymatic systems. Nordlander et al. proposed that asymmetric complexes are not only more appropriate functional models for the active site of phosphoesterase enzymes, but also that they exhibit enhanced catalytic rates compared with their symmetric counterparts [1-3]. A selection of ligands used to generate purple acid phosphatase [1, 4, 5, 6-10], phosphoesterase [11], urease [12, 13], catechol oxidase [14] and manganese catalase biomimetics [15, 16] is displayed in Fig. 7.1. 

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