<b>Deuterium Oxide Solvent Isotope Effects in the Nucleophilic Reactions of Phenyl Esters</b>

Bender, Myron L.; Pollock, Edward J.; Neveu, Maurice C.

doi:10.1021/ja00863a019

Cited by 56 publications

(21 citation statements)

References 1 publication

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“…This result indicates nucleophilic attack by hydroxyl anion toward ,BCDC, because the nucleophilicity of deuteroxide anion is 20-40% higher than hydroxide anion (10)(11)(12)(13)(14)(15). Nucleophilic attack by Aza2bicOct toward f3CDC is ruled out by the D20 effect (16 …”

Section: Resultsmentioning

confidence: 99%

Amine-catalyzed hydrolyses of cyclodextrin cinnamates

Komiyama

Bender

1976

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

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Hydrolyses of 6B-cyclodextrin cinnamate (#CDC) and a-cyclodextrin cinnamate were catalyzed by amines such as 1,4-diazabicyclo(2.2.2)octane, triethylamine, quinuclidine, piperidine, diisobutylamine, and n-butylamine. The rate constant of hydrolyses of the #CDC-amine complexes follows the order: 1,4-diazabicyclo(2.2.2)octane > n-butylamine > quinuclidine > piperidine > triethylamine >> diisobutylamine. The ratio of the catalytic rate constant for the ,8CDC/1,4-diazabi-

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Section: Resultsmentioning

confidence: 99%

Amine-catalyzed hydrolyses of cyclodextrin cinnamates

Komiyama

Bender

1976

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

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“…4, showing the effects of these dyes in the presence and the absence of irradiation. DISCUSSION Thiolesters, while relatively resistant to hydrolysis, are highly susceptible to aminolysis and thiolysis (24)(25)(26)(27) (20) (28), such isotope effects may be interpreted as indicating that general-base catalysis with ratedetermining proton transfer, rather than nucleophilic catalysis, is taking place (29,30).…”

Section: Methodsmentioning

confidence: 99%

On the Mechanism of Action of Choline Acetyltransferase

Currier

Mautner

1974

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

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The substrate specificity of choline acetyltransferase (EC 2.3.1.6) isolated from squid ganglia was investigated. The enzyme catalyzed the acetylation of choline and aminocholine but not of homocholine. In D20 solution there was' considerable slowing of the transacetylation reaction. Photo-oxidation in the presence of methylene blue or rose bengal rapidly inactivated the enzyme, suggesting involvement of a histidine residue in the catalytic site. It seems likely that general-base catalysis by imidazole enhances the ability of enzyme-bound choline (or ammoniumcholine) to react with a thiolester group. Attempts to isolate an acetylthio-enzyme intermediate after incubation with [1ICjacetylcoenzyme A were unsuccessful. A possible mechanism for the' action of choline acetyltransferase is proposed.Since acetylcholine plays an essential part in the permeability changes to cations in excitable membranes encountered during the conduction of the nervous impulse, a great deal of research has been centered on the enzymes responsible for the hydrolysis and the synthesis of this ester, acetylcholinesterase and choline acetyltransferase (ChA), respectively. ChA, the enzyme catalyzing the transfer of the acetyl group of acetylcoenzyme A to choline, has, since its discovery by Nachmansohn and Machado (1) in rabbit brain, been found in a wide variety of sources, including squid head ganglia (2, 3), rat brain (4), bovine brain (5), human placenta (6), and microorganisms (7). However, considerable difficulties were encountered in trying to obtain highly active, homogeneous material, ChA being a rather sluggish enzyme which tends to be unstable and which may exist in multiple forms (8-10). However, recently ChA with an activity of 4,000 smoles/hr per mg was isolated by Husain and Mautner from squid head ganglia (11).While ChA has been known for a long time, a great many questions regarding its mechanism of action remain unanswered. Evidence has been presented that the ChA catalyzed transacetylation from acetylcoenzyme A to choline involves an ordered or a Theorell-Chance mechanism (12-14) with acetylcoenzyme A as the leading substrate. Inhibition studies suggest the involvement of a thiol group in the functions of ChA (4, 15-17). It has also been proposed that imidazole may play a catalytic role in the functions of this enzyme (18,19 Corp.) and prostigmine, bovine serum albumin, ethylenediaminetetraacetate (EDTA), dithiothreitol, NaCl, NaPi, and 10 ;d of ChA (1.8 mg of protein per ml) in the usual amounts (23) with a final volume of 0.2 ml. The samples were incubated at 320 for 30 min; after chromatographic separation, the labeled acetylcholine formed was determined (23) with a Packard Tri-Carb liquid scintillation counter. All determinations were carried out in triplicate, as were controls lacking ChA.Inhibition Assays. Samples contained 50 mM choline, 50 mM inhibitor, 100 mM NaCl, as well as the other components noted above. All assays were carried out in triplicate as were blanks lacking ChA or inhibitor.

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“…Praissman & Rupley (1968) studied the tritium-hydrogen exchange of lysozyme and lysozyme-saccharide complex and found that no profound conformational changes took place in the tritiatedlysozyme. Bender, Pollock & Neveu (1962) investigated the effect of H20 and D20 as a solvent on general base catalysis by imidazole, as well as on nucleophilic catalysis by imidazole. They found that an isotope effect of 2-3 is observed in general base catalysis, which involves as an important step a proton transfer between water and imidazole.…”

Section: Aht=e-rtmentioning

confidence: 99%

Substituent effect on lysozyme-catalysed hydrolysis of some β-aryl di-N-acetylchitobiosides

Tsai

Tang

SubbaRao

1969

Biochemical Journal

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Measurements are reported on the kinetics of the lysozyme-catalysed hydrolysis of several beta-aryl di-N-acetylchitobiosides, some of which have been synthesized for the first time. The catalytic rate constants (k(cat.)) at 45 degrees yield a curved Hammett plot (concave up) and the plot of DeltaH(double dagger) versus DeltaS(double dagger) has a sharp break. Substrates with electron-withdrawing groups exhibit a kinetic deuterium isotope effect (k(H) (cat.)/k(D) (cat.)), whereas those with electron-donating groups show no such isotope effect. The results suggest the operation of different mechanisms for the two types of substrates.

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Deuterium Oxide Solvent Isotope Effects in the Nucleophilic Reactions of Phenyl Esters

Cited by 56 publications

References 1 publication

Amine-catalyzed hydrolyses of cyclodextrin cinnamates

Amine-catalyzed hydrolyses of cyclodextrin cinnamates

On the Mechanism of Action of Choline Acetyltransferase

Substituent effect on lysozyme-catalysed hydrolysis of some β-aryl di-N-acetylchitobiosides

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