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1
Content available Enzymatic oxidation of substituted tryptamines catalysed by monoamine oxidase
Dragulska S., Kańska M.
Nukleonika
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2014
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Vol. 59, No. 3
91--95
EN
The enzymatic deamination of 5-fl uorotryptamine and 5-hydroxytryptamine, 5-HT, catalysed by enzyme monoamine oxidase A (MAO-A, EC 1.4.3.4) was investigated using the kinetic (KIE) and solvent (SIE) isotope effects methods. The numerical values of deuterium isotope effects in the (1R) positions of 5-F-tryptamine were determined using non-competitive spectrophotomeric method. Isotopologue 5-F-[(1R)- -2H]-tryptamine, needed for kinetic studies was obtained by enzymatic decarboxylation of 5'-fl uoro-L-tryptophan, 5'-F-L-Trp, in fully deuteriated medium.
2
Content available Enzymatic oxidation of substituted tryptamines catalysed by monoamine oxidase
Dragulska S., Kańska M.
Nukleonika
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2014
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Vol. 59, No. 2
s. 91--95
EN
The enzymatic deamination of 5-fl uorotryptamine and 5-hydroxytryptamine, 5-HT, catalysed by enzyme monoamine oxidase A (MAO-A, EC 1.4.3.4) was investigated using the kinetic (KIE) and solvent (SIE) isotope effects methods. The numerical values of deuterium isotope effects in the (1R) positions of 5-F-tryptamine were determined using non-competitive spectrophotomeric method. Isotopologue 5-F-[(1R)- -2H]-tryptamine, needed for kinetic studies was obtained by enzymatic decarboxylation of 5'-fl uoro-L-tryptophan, 5'-F-L-Trp, in fully deuteriated medium.
3
Content available Deuterium isotope effects in oxidation of dopamine by tyramine oxidase
Pająk M., Byszewska W., Kańska M.
Nukleonika
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2013
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Vol. 58, No. 2
255--259
EN
We report the studies on the mechanism of oxidation of dopamine (DA) to 3’,4’-dihydroxyphenylacetaldehyde (DOPAL) by enzyme tyramine oxidase (EC 1.4.3.6) using kinetic isotope effects (KIE) and solvent isotope effects (SIE) methods. For kinetic studies, the selectively deuterium labelled isotopologues of dopamine, i.e., [(1R)-2H]-, and [(1S)- -2H]-DA were used. The numerical values of KIE’s for the (1R)- and (1S)-isotopologues of dopamine in the enzymatic oxidation of DA to DOPAL were determined using the non competitive spectrophotometric method. Also, the SIE’s for this reaction carried out in heavy water were obtained spectrophotometrically. Some mechanistic details of enzymatic oxidation of DA to DOPAL were discussed.
4
Content available Deuterium isotope effects in oxidation of dopamine and norepinephrine catalyzed by horseradish peroxidase
Byszewska W., Pająk M., Kańska M.
Nukleonika
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2013
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Vol. 58, No. 4
475--479
EN
Deuterium kinetic isotope effects (KIE’s) in the reaction of oxidation of dopamine (DA) catalyzed by the enzyme horseradish peroxidase (HRP, EC 1.11.1.7) was determined using a non-competitive spectrophotometric method. For kinetic studies, the deuterium ring labelled isotopomer [2’,5’,6’-2H3]-dopamine was synthesized using acid catalyzed isotopic exchange between authentic dopamine and heavy water. Deuterium solvent isotope effects (SIE’s) for dopamine and norepinephrine were determined separately for the enzymatic oxidation carried out in the presence or absence of hydrogen peroxide. Some mechanistic details of enzymatic oxidation of dopamine and norepinephrine to corresponding catecholchromes catalyzed by HRP were discussed.
5
Content available Isotope effects in chemistry
Van Hook W. A.
Nukleonika
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2011
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Vol. 56, No. 3
217-240
EN
Isotope effects on chemical equilibria, reaction rates and molecular properties are reviewed together with the theoretical formalism for understanding such effects.
6
Content available Isotope effects on selected physicochemical properties of nitromethane and 1-pentanol
Makowska A., Szydłowski J.
Nukleonika
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2006
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Vol. 51,suppl.2
81-85
EN
Densities, kinematic viscosities, speed of sound and refractive indices of nitromethane and 1-pentanol and their deuterated derivatives CD3NO2 and C5H11OD were measured. The data obtained allowed to calculate molar volumes, dynamic viscosities, isentropic compressibilities and isobaric thermal expansion. Deuterium isotope effect on the selected physicochemical properties of both nitromethane and 1-pentanol has been determined. Large isotope effects characterizing density, viscosity and speed of sound are observed for nitromethane and much smaller for 1-pentanol. Isotope effects on molar volume are small both for nitromethane and 1-pentanol, but of the opposite sign. These observations are in agreement with the expectations.
7
Content available Multiple isotope effects as a probe of the tartrate dehydrogenase-catalyzed oxidative decarboxylation of D-malate
Karsten W., Cook P.
Nukleonika
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2002
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Vol. 47,suppl.1
13-15
EN
A change in the dinucleotide reactant from NAD+ to the more oxidizing APAD+ in the malic enzyme reaction results in a change in the mechanism of oxidative decarboxylation of malate from stepwise to concerted [7]. In order to determine whether this is a phenomenon general to metal ion dependent â-hydroxyacid oxidative decarboxylases, tartrate dehydrogenase, which catalyzes a reaction diastereotopic to malic enzyme, was studied using the technique of multiple isotope effects. A primary deuterium isotope effect of 1.41 on V/Kmalate was measured, as well as a primary 13C-isotope effect of 1.0096. A decrease in the measured value of the 13C-isotope effect to 1.0078 is consistent with a stepwise mechanism, as observed for malic enzyme. The 13C-isotope effect with thioNAD+ also decreases from a value of 1.0053 using D-malate to 1.0009 using D-malate-2-D, consistent with stepwise oxidative decarboxylation with this alternative dinucleotide substrate. The data suggest that the change
8
Content available Mechanistic variation in the glycosyltransfer of N-acetylneuraminic acid
Horenstein B., Yang J., Bruner M.
Nukleonika
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2002
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Vol. 47,suppl.1
25-28
EN
N-acetylneuraminic acid is an acidic nine-carbon amino ketose typically found at the non-reducing terminus of glycoproteins and glycolipids. The presence of a carboxylate group adjacent to the anomeric center suggest that this sugar could have transition states with highly stabilized oxocarbenium ion character during transfer reactions at the anomeric carbon. Kinetic isotope effect (KIE) experiments were used to probe the transition state for solvolysis of UMP-NeuAc, sialyltransferase-catalyzed transfer of UMP-NeuAc to N-acetyl-lactosamine, trans-sialidase catalyzed transfer of alfa(2--3) Neu-Lac or alfa(2--3) Neu-Gal, and acid catalyzed hydrolysis of alfa(2--3) Neu-Lac. The two key positions of isotope substitution in the N-acetyl neuraminic acid residue were the C3’ position, di-substituted with deuterium, and the C2’ position, substituted with either carbon-13 or carbon-14. The solvolysis reaction had a beta–2H KIE of 1.28 and a primary 14C KIE of 1.03. The sialyltransferase-catalyzed reaction had a b-2H KIE of 1.22 and a 14C KIE of 1.03. Trans-sialidase had a b–2H KIE of 1.05 and a primary 13C KIE of 1.03, equivalent to a 14C KIE of 1.06. Solvolysis of the trans-sialidase substrate gave a beta-2H KIE of 1.06, and a primary 13C KIE of 1.015. The results indicate a very late transition state for solvolysis of CMP-NeuAc, without nucleophilic participation. The sialyltransferase transition state is similar, but with less charge development. Trans-sialidase has a transition state with diminished charge development and considerable nucleophilic character, which leads to a covalent intermediate. The glycosyltransfer of N-acetylneuraminic acid glycosides is not limited to the classical dissociative mechanism.
9
Content available Isotope effects on vapor phase 2nd virial coefficients
Van Hook W., Rebelo L., Wolfsberg M.
Nukleonika
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2002
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Vol. 47,suppl.1
47-51
EN
Vapor phase 2nd virial coefficient isotope effects (VCIE's) are interpreted. A useful correlation is developed between -Delta(Beta-bo)/(Beta-bo) = (-VCIE) and the reference condensed phase reduced isotopic partition function ratio [ln(fc/fg)]*. B is the second virial coefficient, bo = 2pi sigma3/3, sigma is the Lennard-Jones size parameter, and Delta is an isotopic difference, light-heavy. [ln(fc/fg)]* can be obtained from vapor pressure isotope effects for T/TCRITICAL < 0.7. Also (-VCIE) = ln(fp/fg 2), where ln(fp/fg 2) is the reduced isotopic partition function ratio describing the equilibrium between monomers and interacting pairs. At temperatures well removed from crossovers in ln(fp/fg 2) or [ln(fc/fg)]*, ln(fp/fg 2) = (0.4š0.2) [ln(fc/fg)]*.
10
Deuterium isotope fractionation between ortho-alkyl substituted phenols and t-butylthiol in oxygen bases
Wawer A., Jelińska-Kazimierczuk M., Szydłowski J.
Polish Journal of Chemistry
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1998
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Vol. 72, nr 3
618-626
EN
Equilibrium isotope effect in the exchange reaction of deuterium between phenol (P), 2-isopropylphenol (IPP), 2,6-diisopropylphenol (DIPP), 2,6-ditertbutyl phenol (DTBP) and tertbutylthiol (TBT) has been studied at 298 K. The fractionation factors (alpha) have been measured in cyclohexane and carbon tetrachloride solution and in a few oxygen bases: acetone, 1,4-dioxane, ethyl formate, ethyl ether, tetrahydrofurane, N,N-dimethylformamide, dimethylsulphoxide and hexamethylphosphoramide. Using chemical shifts of phenol OH protons, the thermodynamic parameters of complex formation with the oxygen bases have been determined. The experimental data show that ln alpha correlates with the formation enthalpy of the phenol-oxygen base complex in DIPP-TBT-base system but there is no simple correlation in IPP-TBT-base system. Futhermore it was found that in DTBT-TBT-base system ln alpha depends linearly on the basicity of the (solvent DN parameters). On the other hand, ln alpha correlates with acidic parameters of the solvents (AN) in IPP-TBT-base and P-TBT-base systems. All above correlations are explained by taking into account two competition processes: selfassociation of phenol molecules and their solvation by oxygen bases.
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