Phenylphosphate

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 anaerobic metabolism of phenol in T. aromatica is initiated by the ATP-dependent conversion of phenol to phenylphosphate catalyzed by phenylphosphate... 

Phenylphosphate synthase consists of three subunits with molecular masses of 70, 40, and 24kDa. Subunit 1 resembles the central part of classical phospho-enolpyruvate synthase which contains a conserved histidine residue. It catalyzes the exchange of free [ C] phenol and the phenol moiety of phenylphosphate but not the phosphorylation of phenol. Phosphorylation of phenol requires subunit 1, MgATP, and another protein, subunit 2 (40kDa), which resembles the N-terminal part of phosphoenolpyruvate synthase. Subunit 1 and 2 catalyze the following reaction ... 

The phosphoryl group in phenylphosphate is derived from the -phosphate group of ATP. The free energy of ATP hydrolysis obviously favors the trapping of phenol K, 0.04 mM), even at a low ambient substrate concentration. The reaction is stimulated several fold by another protein, subunit 3 (24kDa). The molecular and catalytic features of phenylphosphate synthase resemble those of phosphoenolpyruvate synthase, albeit with interesting modifications. ... 

The purified E. cloacae P240 4-hydroxybenzoate decarboxylase did not catalyze the carboxylation of phenylphosphate, indicating phenolphosphate... 

Primary structure analysis of phenylphosphate carboxylase of T. aromatica is performed in detail, to clarify the reaction mechanism involving four kinds of subunits. The a, (3, y, 8 subunits have molecular masses of 54, 53, 18, and lOkDa, respectively, which make up the active phenylphosphate carboxylase. The primary structures of a and (3 subunits show homology with 3-octaprenyl-4-hydroxybenzoate decarboxylase, 4-hydroxybenzoate decarboxylase, and vanil-late decarboxylase, whereas y subunit is unique and not characterized. The 18kDa 8 subunit belongs to a hydratase/phosphatase protein family. Taking 4-hydroxybenzoate decarboxylase into consideration, Schiihle and Fuchs postulate that the a(3y core enzyme catalyzes the reversible carboxylation. ... 

Schiihle K, G Fuchs (2004) Phenylphosphate carboxylase a new C-C lyase involved in anaerobic phenol metabolism in Thauera aromatica. J Bacterial 186 4556-4567. 

Narmandakh A, N Gad on, F Drepper, B Knapp, W Haehnel, G Fuchs (2006) Phosphorylation of phenol by phenylphosphate synthase role of histidine phosphate in catalysis. J Bacteriol 188 7815-7822. 

The metabolism of phenols under anaerobic conditions has been examined under denitrifying, sulfate-reducing, Fe (lll)-reducing, and anaerobic nonmethanogenic conditions. It is plausible to suggest a common pathway that has been elucidated for denitrifying bacteria. This comprises (a) activation of phenol by the formation of phenylphosphate, (b) carboxylation at a position para to... 

Similarly, cyclodextrin accelerates the cleavage of pyrophosphates by about 200-fold. This enhancement is associated with a simultaneous transfer of a phenylphosphate group to the host by the vicinal action of the hydroxy groups [see Figure 5.4] (Hennrich Cramer, 1965). In this case the product monophenylphosphate also forms an inclusion complex and thus product inhibition occurs. Because of this, the system is not truly catalytic. 

Series of various mono,- bi-, and poly-(thio)urea-functionalized (poly)saccha-rides have already been synthesized and studied for molecular recognition of, e.g., dimethyl and phenylphosphate as model compounds for monoanionic and polyanionic phosphate esters, respechvely [111]. Thiourea derivatives such as 195-197 were analyhcally identified to provide double hydrogen bonding mediated host-guest complexes of well-defined dimension and orientations and were also reported to serve as phosphate binders even in the hydrogen bonding environment of water (Figure 6.57) [111]. 

Disodium phenylphosphate (2H2O) [3279-54-7] M 254.1. Dissolved in a minimum amount of methanol, filtering off an insoluble residue of inorganic phosphate, then ppted by adding an equal volume of ethyl ether. Washed with ethyl ether and dried [Tsuboi Biochim Biophys Acta 8 173 7952]. 

P 13.9 Base-Catalyzed Hydrolysis of Diethyl Phenylphosphates Mechanistic Considerations Using LFERs... 

Figure 15. Inhibition of the reaction between p-nitrophenyl acetate and HSA by a mono- and dianion. Increasing amounts of the monoanion, phenylmethylphosphonate (O), and the dianion, phenylphosphate (D), were added to a solution of 3.5 X 10 5M HSA in pH 8.0, 0.06M triethanolamine /HCl at 25°C.

The affinity of this site for anions presumably reflects its content of one or more cationic groups. To characterize this cationic center we have compared the inhibitory effects of a number of different kinds of anions. Figure 15 shows the effect of two closely related anions, phenylphosphate, a dianion at pH 8.0, and phenylmethylphosphonate, a monoanion under the same conditions, on the reaction between HSA and p-nitrophenyl acetate. Only the latter compound is inhibitory which along with other results suggests that the site is specific for monoanions. 

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