Stereochemical, mechanistic, and structural features of enzyme-catalysed phosphate monoester hydrolyses

Gani, D.; Wilkie, John

doi:10.1039/cs9952400055

Cited by 68 publications

(69 citation statements)

References 23 publications

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“…(18,19), is seen to enhance the rate of water attack on the dianionic substrate by a factor of Ϸ10 21 and to bind the altered substrate in the transition state with a formal dissociation constant of Ϸ10 Ϫ26 M. These rate enhancements and catalytic proficiencies exceed even those of decarboxylases acting on orotidine 5Ј-phosphate (OMP) and amino acids, the most proficient enzymes identified thus far (Fig. 3).…”

Section: Resultsmentioning

confidence: 92%

The rate of hydrolysis of phosphomonoester dianions and the exceptional catalytic proficiencies of protein and inositol phosphatases

Lad

Williams

Wolfenden

2003

Proc. Natl. Acad. Sci. U.S.A.

258

349

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To evaluate the proficiency of phosphatases as catalysts, the rate of the uncatalyzed hydrolysis of simple phosphate monoester dianions was estimated by extrapolating rates measured over a range of high temperatures. The rate of spontaneous hydrolysis of phenyl phosphate dianion indicates that a linear free energy relationship reported earlier is reliable for leaving groups whose conjugate acids have pKa values up to at least 10. Using Teflon reaction vessels, it proved possible to follow the hydrolysis of methyl phosphate and 3-(4-carboxy)-2,2-dimethylpropyl phosphate in strong alkali. Even in 1 M KOH, the reaction was found to be specific acid catalyzed. These results establish an upper limit for dianion reactivity, which had been overestimated earlier as a result of the leaching by alkali of silicic acid from quartz reaction vessels. The present findings indicate that the half-time for attack by water on alkyl phosphate dianions is 1.1 ؋ 10 12 years (k ‫؍‬ 2 ؋ 10 ؊20 s) at 25°C and that phosphatases involved in cell signaling and regulation produce the largest rate enhancements that have been identified thus far. Protein phosphatase-1 and inositol 1-phosphatase exceed all other known enzymes in their affinities for the altered substrates in the transition state.M ost enzyme reactions proceed with k cat ͞K m values in the neighborhood of 10 7 M Ϫ1 ⅐s Ϫ1 and appear to be similarly efficient according to that criterion. However, to assess the proficiency of an enzyme as a catalyst, and its corresponding affinity for the altered substrate in the transition state, it is necessary to compare k cat ͞K m with the rate constant of the corresponding reaction under the same conditions in the absence of a catalyst. In contrast to the relatively narrow range of values of k cat ͞K m observed for enzyme catalyzed reaction rates, the rates of these uncatalyzed reactions span a range of at least 19 orders of magnitude (1). Thus, differences in enzyme proficiency tend to reflect differences in the rates of the uncatalyzed reactions rather than the catalyzed reactions, and enzymes differ greatly from one another in their prowess as catalysts. Enzymes that catalyze the slowest reactions are of practical interest, in that they offer sensitive targets for inhibition by transition-state analogues. Their mechanisms of action are also particularly challenging to rationalize. Conspicuous among these slow reactions is the hydrolysis of monoesters of phosphoric acid.In biological systems, phosphate monoesters are cleaved by two groups of monoesterases that act by different mechanisms.One group of phosphomonoesterases, typified by bacterial alkaline phosphatase (2) and protein tyrosine phosphatases (3), uses an active-site nucleophile to displace the alcohol-leaving group from the substrate to form a phosphoryl-enzyme intermediate, which is subsequently hydrolyzed. Rate enhancement by enzymes that act through a double-displacement mechanism is not simple to analyze in terms of transition-state affinity or transition-state stabilization (...

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Section: Resultsmentioning

confidence: 92%

The rate of hydrolysis of phosphomonoester dianions and the exceptional catalytic proficiencies of protein and inositol phosphatases

Lad

Williams

Wolfenden

2003

Proc. Natl. Acad. Sci. U.S.A.

258

349

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“…Este arranjo promove um aumento da eletrofilicidade do átomo de fósforo através da coordenação do íon metálico a um dos átomos de oxigênio do fosfato. Por outro lado, posiciona favoravelmente o hidróxido metálico para o ataque equatorial 48 . (2), mas não têm efeito sobre a velocidade de hidrólise do bis(6-hidroxiquinolina)fosfato (3).…”

Section: Catálise Por íOns Metálicosunclassified

A química dos ésteres de fosfato

Domingos¹,

Longhinotti²,

Machado³

et al. 2003

Quím. Nova

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Recebido em 5/11/02; aceito em 29/1/03 THE CHEMISTRY OF PHOSPHATE ESTERS. This work summarizes important aspects of the chemistry of phosphate esters, with special emphasis on: i) advances in the design of enzymatic models for phosphatases; and ii) nerve agents and currently used strategies for detoxification. The physical organic chemical aspects that are responsible by the reactivity of phosphate esters are also discussed.Keywords: phosphate esters; nerve agents; enzymatic models. INTRODUÇÃOO fósforo é um elemento vital na composição da matéria viva e não se conhece um organismo vivo que não utilize a química deste elemento. Os animais absorvem o fósforo a partir do alimento ingerido e grande parte do P encontra-se nos mesmos como "fosfato orgânico", nas formas de mono e diésteres (ligações C-O-P). Além de fosfatos orgânicos há polifosfatos inorgânicos e uma variedade de compostos importantes com ligações N-P (fosfocreatinina, fosfoarginina), bem como em microorganismos têm sido caracterizados compostos contendo ligações P-C 1 . O corpo humano contém aproximadamente 1% em massa deste elemento e, embora esta quantidade de fósforo orgânico seja pequena, seu papel é essencial nos processos celulares. Os ésteres fosfóricos são os principais responsáveis pelo armazenamento e transmissão de informação genética (os fosfodiésteres DNA e RNA) 2 , participam na estrutura de várias coenzimas 3 e, anidridos fosfóricos e compostos orgânicos contendo ligações N-P servem como principal reserva de energia [trifosfato de adenosina (ATP), creatina fosfato, acetilfosfato (AcP), fosfoenolpiruvato e polifosfato inorgânico] 4,5 . Além da sua importância em processos biológicos, os ésteres fosfóricos encontram aplicações como plastificantes, reagentes na preparação de polímeros organofosforados, complexantes para a extração de cátions de metais pesados, inseticidas, pesticidas e compostos tóxicos utilizados em armas de guerra 6 . Os ésteres fosfóricos são extremamente numerosos e podem ser classificados em mono-, di-e triésteres, de acordo com o número de grupos ésteres presentes, sendo que os triésteres não participam em processos biológicos. Os mono-e diésteres do ácido fosfórico contêm grupos hidroxila na sua estrutura caracterizando-se, portanto, como ésteres com uma funcionalidade adicional equivalente à de ácidos dipróticos ou monopróticos, respectivamente.A solução encontrada pela natureza para garantir aos seres vivos a sua perpetuação deu-se pelo uso das ligações P-O para formar os fosfodiésteres DNA e RNA. A evolução encontrou esta ligação como a ideal para este propósito devido à estabilidade dos diésteres de fosfato. É interessante observar que compostos organofosforados foram selecionados pelo homem para desenvolver pesticidas, inseticidas e gases de guerra. As ligações P-O são ideais para o desenho destas classes de compostos, já que os tornam resistentes à ação da água, do solo e do ar, a fim de que possam atingir o seu alvo sem serem alterados quimicamente, ficando aptos para acumular nos tecidos e provocar danos aos...

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“…Most zinc enzymes are classified as hydrolyases because they catalyze the hydrolysis of condensed bonds present in many tissues which are most associated with proteins like esters (both phosphate and carboxylate), pyrophosphate and various types of peptides (Emsely 2001, Gani & Wilkie 1995, Lipscomb & Strater 1996, Wilcox 1996.…”

Section: Introductionmentioning

confidence: 99%

Macrocyclic Zn(II) Complexes: Synthesis, Structure and Hydrolysis of p-Nitrophenyl Acetate (pNPA)

Pandey

Sharma

Pandey

et al. 2015

J. Inst. Sci. Tech.

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A new series of Zn(II) macrocyclic complexes has been synthesized by the reaction of Schiff bases (derived from dihydrazides and benzil/phthalaldehyde) in the presence of zinc(II) acetate dihydrate in ethanol. The complexes have been characterized by means of elemental and spectral (IR, 1 H and 13 C NMR) and SEM analysis. The kinetic studies were done to study the catalytic properties of these complexes towards the hydrolysis of p-nitrophenylacetate (pNPA) at 25°C in aqueous dimethylsulphoxide using phosphate buffer (pH = 7.0-8.5). During the reaction, absorbance of p-nitrophenolate increases with increase in time (i.e., increase of p-nitrophenolate concentration) which give information about the reaction progress i.e., ester hydrolysis. On the basis of these results, a plausible mechanism for the hydrolysis of pNPA is proposed. It is observed that coordinated water molecule might be serving as a good nucleophile that effectively catalyzes pNPA hydrolysis. Therefore, this type of complexes can be used as hydrolytic model enzymes.

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Stereochemical, mechanistic, and structural features of enzyme-catalysed phosphate monoester hydrolyses

Cited by 68 publications

References 23 publications

The rate of hydrolysis of phosphomonoester dianions and the exceptional catalytic proficiencies of protein and inositol phosphatases

The rate of hydrolysis of phosphomonoester dianions and the exceptional catalytic proficiencies of protein and inositol phosphatases

A química dos ésteres de fosfato

Macrocyclic Zn(II) Complexes: Synthesis, Structure and Hydrolysis of p-Nitrophenyl Acetate (pNPA)

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